Name: versatile co2 transformations into complex products: a one-pot two-step strategy
Uploaded: 2019-11-09T14:00:00.000+00:00
Duration: 7 min 36 s
Description: Watch this Scientific Journal Video about Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy at JoVE.com

S. D. thanks R&#233;gion Midi-Pyr&#233;n&#233;es and Universit&#233; F&#233;d&#233;rale de Toulouse for doctoral fellowship. D. Z. thanks Chinese Scholarship Council for doctoral fellowship. A. M. thanks COLFUTURO for doctoral fellowship. S. B. thanks the ANR programme JCJC &#34;ICC&#34; and Prof. A. Leon for fruitful discussion.

CAUTION: Please consult material safety data sheets (MSDS) of the chemicals before use. Please use appropriate safety practices when performing the following reactions and personal protective equipment. A special attention must be dedicated to the use of the vacuum line and gas pressure system.
1. Synthesis of compound 2 from CO2 in a nuclear magnetic resonance (NMR) tube
<ol>
	<li>Stock solution of Fe(H)2(dmpe)2: dissolve 4.6 mg of Fe(H)2(dmpe)221,22 in 1 mL of tetrahydrofuran (THF)-d8. 
	NOTE: dmpe = 1,2-bis(dimethylphosphino)ethane</li>
	<li>In a glove box, charge an NMR tube with 15.9 mg of 9-borabicyclo[3.3.1]nonane (9-BBN) and 100 &#181;L of a stock solution of Fe(H)2(dmpe)2 (1 mol%).</li>
	<li>Add 0.5 mL of tetrahydrofuran (THF)-d8.</li>
	<li>Close the tube and bring it outside the glove box.</li>
	<li>Connect the tube to a gas system and place it at 25 &#176;C for 15 min to equilibrate the temperature of the solution inside the tube. 
	NOTE: The gas system connects the CO2 bottle to both the vacuum line and the NMR tube. The connections are with Teflon tube and Swadgelock connectors (see Figure 1 for a scheme of the setup). This system enables to add the pressure defined at the regulator at the desired temperature.</li>
	<li>Add 1 atm of CO2.</li>
	<li>Leave for 3 min under a dynamic pressure of CO2 and close the tube.</li>
	<li>Leave the tube at 25 &#176;C for 45 min. 
	NOTE: At this step bis(boryl)acetal 1 is generated inside the NMR tube in 85% yield (see representative results for the NMR analysis).</li>
	<li>Stock solution of amine: dissolve 177.3 mg of 2,6-(diisopropyl)phenylamine in 1 mL of THF-d8.Once compound 1 is generated, open the NMR tube inside a glove box and add 55 &#181;L of a stock solution of the 2,6-(diisopropyl)phenylamine, corresponding to 1 equivalent of the generated bis(boryl)acetal 1.</li>
	<li>Close the tube and hand shake it for 10 s.</li>
	<li>After 20 min, confirm the formation of imine 2 by 1H NMR analysis (Figure 2). Use hexamethylbenzene (roughly 10 mol% vs 9-BBN) as an internal standard to determine the NMR yield.</li>
</ol>
2. Synthesis of compound 3 from CO2 in a Fisher Porter
<ol>
	<li>Charge a Fisher Porter with 320 mg of 9-BBN, 9.4 mg of Fe(H)2(dmpe)2 and a magnetic stirring bar21,22.</li>
	<li>Add 10 mL of THF.</li>
	<li>Close the Fisher Porter and bring it outside the glove box.</li>
	<li>Place it at 25 &#176;C for 15 min to equilibrate the temperature of the solution.</li>
	<li>Connect the Fisher Porter to the gas system and add 1 atm of CO2. 
	NOTE: The gas system connects the CO2 bottle to both the vacuum line and the Fisher Porter. The connections are with Teflon tube and Swadgelock connectors (see Figure 1 for a scheme of the setup). This system enables to add the pressure defined at the regulator at the desired temperature.</li>
	<li>Leave for 3 min under a dynamic pressure of CO2, close the tube and stir it at 25 &#176;C for 45 min. 
	NOTE: This stage corresponds to the selective generation of bis(boryl)acetal 1 from CO2 hydroboration in 85% yield.</li>
	<li>After 45 min, open the Fisher Porter in a glove box and add a solution of 380 mg of triazol-5-ylidene in 6 mL of THF.</li>
	<li>Outside the glove box, charge the Fisher Porter with 3 atm of CO2.</li>
	<li>Stir the solution at 60 &#176;C for 60 min under a dynamic pressure of 3 atm of CO2.</li>
	<li>Let the solution cool down to room temperature.</li>
	<li>Remove the volatiles under vacuum and wash the residue with 3x 2 mL of diethylether (Et2O) at 0 &#176;C to obtain CO2 adduct 3 as a white powder (Figure 3).</li>
	<li>To generate monocrystals, place a concentrated THF/pentane solution at -37 &#176;C for 24-48 h.</li>
</ol>
3. Synthesis of compound 4 from CO2 in a Fisher Porter
<ol>
	<li>In a glove box, charge a Fisher Porter tube with 159 mg of 9-BBN, 4.7 mg (1 mol%) of Fe(H)2(dmpe)2 and a magnetic stirring bar.</li>
	<li>Add 5 mL of THF.</li>
	<li>Close the Fisher Porter and bring it outside the glove box.</li>
	<li>Place it at 25 &#176;C for 15 min to equilibrate the temperature of the solution.</li>
	<li>Connect the Fisher Porter to the gas system and add 1 atm of CO2.</li>
	<li>Leave 3 min under a dynamic pressure of CO2, close the Fisher Porter and stir it at 25 &#176;C for 45 min. 
	NOTE: This stage corresponds to the selective generation of bis(boryl)acetal 1 from CO2 hydroboration in 85% yield.</li>
	<li>After the generation of 1, open the Fisher Porter in a glove box and add 54 mg of triazol-5-ylidene.</li>
	<li>Outside the glove box, stir the solution at 80 &#176;C for 40 min to generate a mixture of compounds containing compound 4.</li>
	<li>Remove the solvent and dissolve part of the residue in 0.6 mL of THF-d8.</li>
	<li>Filtrate the solution with a syringe equipped with a PTFE filter (0.2 &#181;m) and place it in an NMR tube for analysis. Use hexamethylbenzene (roughly 10 mol% vs 9-BBN) as an internal standard to determine the NMR yields.</li>
</ol>
4. Alternative synthesis of compound 4 from d,l-Glyceraldehyde
<ol>
	<li>In a glove box, charge a Schlenk tube with 50 mg of d,l-Glyceraldehyde, 135 mg of 9-BBN and a magnetic stirring bar.</li>
	<li>Add 4 mL of THF. 
	CAUTION: Upon dissolution of the compound, H2 evolution occurs.</li>
	<li>Close the Schlenk with a septum and stick a needle into it to allow the constant release of H2 formed.</li>
	<li>Stir the white suspension at room temperature for 24 h inside the glove box.</li>
	<li>Add 165 mg of triazol-5-ylidene.</li>
	<li>Stir 3 h at room temperature. All residues solubilize during that time.</li>
	<li>Remove the volatiles under vacuum.</li>
	<li>Solubilize the residue in a minimum amount of Et2O (1 mL) and place the solution at -37 &#176;C for 12 h.</li>
	<li>Compound 4 precipitates. Remove the filtrate by filtration and dry the precipitate under vacuum.</li>
	<li>Isolate compound 4 as a white powder in 72% yield.</li>
</ol>

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The authors have nothing to disclose.

Herein, we present the one-pot two-step versatile transformations of CO2 into complex products. The first step of the method concerns the selective 4 e- reduction of CO2 with a hydroborane reductant. This step is critical because selectivity toward the 4 e- reduction is challenging. Very few systems have been reported that describe the selective generation of bis(boryl)acetal23,24,25. In our case, an iron hydride complex catalyzes this selective 4 e- reduction of CO2 with 9-BBN, affording compound 1, under mild conditions (25 &#176;C) and with very short reaction time (45 min) (Figure 2)18. Our study shows that the reaction conditions are very important. In our hand, each attempt to change the concentration, solvent, CO2 pressure and temperature led to the decrease of the yield in compound 1. A longer reaction time is also detrimental because it leads to over-reduction to the methanol level or evolution of the bis(boryl)acetal into several oligomeric compounds. From our experience, it is necessary to verify the outcome of this reduction step by in situ 1H NMR characterization. The reproducibility of the method needs to be probed over several runs.
The in situ condensation reaction of the intermediate 1 with a bulky aniline gives rise to the corresponding imine 2 (Figure 2). This is a straightforward method and compound 2 is readily formed in a high yield (83%). This reaction can also be used to probe the efficiency of the reduction step. This method is the only method enabling the synthesis of imine function from CO2. Moreover, intermediate 1 was proved to be a versatile source of methylene in various condensation reactions leading to the formation of C-N, C-O, C-C and C=C bonds18. This method thus offers a straightforward way of using CO2 as a surrogate of formaldehyde in condensation reactions26.
Intermediate 1 reacts with Ender&#39;s carbene to afford compounds 3 or 4, depending on the reaction conditions (Figure 3)20. With the support of in-depth experimental and theoretical study, we were able to explain the observed reactivity. In this case, compound 1 does not react as formaldehyde since boryl moieties remain in compounds 3 and 4. This feature arises from the formation of an unprecedented O-Borylated Breslow intermediate (Figure 3)27,28,29,30,31,32. This intermediate is not observed experimentally but may act as a bifunctional Lewis acid/Lewis base activator toward CO2 to afford compound 3 or leads to the homocoupling of two more carbon centers to afford compound 4. In both products, chiral centers are generated and in the case of compound 4, the two chiral centers, C2 and C3, are obtained in a diastereoselective manner, thanks to the presence of the bridging boryl fragment.
The advances presented herein were possible thanks to the one-pot two-step method employed and to the high and versatile reactivity of intermediate 1 generated from the selective 4e- reduction of CO2. Following a similar method to further improve the scope and the complexity of the synthesized molecules, on-going works are dedicated i) to tune the properties of bis(boryl)acetal in using other hydroborane reductants and ii) to probe different coupling conditions in using other organo-catalysts.

In light of the large interest in using CO2 as a sustainable carbon source1,2,3, the purpose of the method is to transform CO2 into a variety of value-added products.
Intense researches aim at functionalizing CO24,5 or reducing it into formic acid (2 e- reduction), carbon monoxide (2 e- reduction), methanol (6 e- reduction) or methane (8 e- reduction)1,6. The interception of the 2 e- reduction product with amine, notably, gives rise to formamide and methylamine7,8,9. These areas of research are the most advanced so far. However, the scope of accessible functions and the added value of products formed compared to the starting materials remains rather minimal.
To circumvent this limitation, we focused i) on the 4 e- reduction of CO2 and ii) on applying a one-pot two-step procedure. The interest of the one-pot two-step procedure is to limit compatibility issues between the two steps and consequently to broaden the type of reactivity which could be conducted after the first step of reduction. We targeted the 4 e- reduction of CO2 because formaldehyde -the simplest 4 e- reduction product- is a particularly reactive and versatile carbon source10,11. It is used in condensation reaction as a methylene source and can be polymerized into carbohydrates. The latter -called formose reaction- is an impressive transformation generating carbon chain and chiral carbon centers solely from formaldehyde and is of high interest for synthetic-12,13 and prebiotic-chemistry14,15,16.While we are able to observe free formaldehyde from CO2 hydroboration17, its selective generation under homogeneous conditions is still unprecedented. Instead of formaldehyde, we developed the synthesis of bis(boryl)acetal compound 1 from the selective double hydroboration of CO218,19.
In one-pot two step processes we prove herein that, in the same pot, this intermediate 1 i) reacts as a surrogate of formaldehyde in condensation reactions18 or ii) gives rise to a modified formose-type reaction20. In this latter reaction, C-C coupling and chiral carbon centers are obtained.

<table><tbody><tr><td>Wilmad quick pressure valve NMR tube 5 mm diam.</td><td>Sigma-Aldrich</td><td>Z562882-1EA</td><td></td></tr><tr><td>Filtre-seringue PTFE hydrophobe &amp;Oslash; 25 mm pores 0,22 &amp;micro;m</td><td>UGAP</td><td>2528593</td><td></td></tr><tr><td>Fisher Porter</td><td>Home made system</td><td></td><td></td></tr><tr><td>9-borabicyclo[3.3.1]nonane dimer</td><td>Sigma-Aldrich</td><td>178713</td><td></td></tr><tr><td>FeCl&lt;sub&gt;2&lt;/sub&gt; (anhydrous)</td><td>Strem</td><td>MFCD00011004</td><td></td></tr><tr><td>d,l-Glyceraldehyde</td><td>Sigma-Aldrich</td><td>G5001</td><td></td></tr><tr><td>2,6-(diisopropyl)phenylamine</td><td>Sigma-Aldrich</td><td>374733</td><td></td></tr><tr><td>dimethylphosphinoethane</td><td>Strem</td><td>MFCD00008511</td><td></td></tr><tr><td>Tetrahydrofuran</td><td>Carlo Erba</td><td></td><td>solvent</td></tr><tr><td>Diethyl ether</td><td>Carlo Erba</td><td></td><td>solvent</td></tr><tr><td>Pentane</td><td>Carlo Erba</td><td></td><td>solvent</td></tr><tr><td>Tetrahydrofuran D8</td><td>Eurisotop</td><td>D149FE</td><td></td></tr></tbody></table>

versatile co2 transformations into complex products: a one-pot two-step strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products and notably to generate chiral carbon centers. The crucial first step consists in the selective double hydroboration of CO2 catalyzed by an iron hydride complex. The product obtained with this 4 e- reduction is a rare bis(boryl)acetal, compound 1, which is subjected in situ to three different reactions in a second step. The first reaction concerns a condensation reaction with (diisopropyl)phenylamine affording the corresponding imine 2. In the second and third reaction, intermediate 1 reacts with triazol-5-ylidene (Enders&#39; carbene) to afford compounds 3 or 4, depending on the reaction conditions. In both compounds, C-C bonds are formed, and chiral centers are generated from CO2 as the only source of carbon. Compound 4 exhibits two chiral centers obtained in a diastereoselective manner in a formose-type mechanism. We proved that the remaining boryl fragment plays a key role in this unprecedented stereocontrol. The interest of the method stands on the reactive and versatile nature of 1, giving rise to various complex molecules from a single intermediate. The complexity of a two-step method is compensated by the overall short reaction time (2 h for the larger reaction time), and mild reaction conditions (25 &#176;C to 80 &#176;C and 1 to 3 atm of CO2).

Successful generation of bis(boryl)acetal compound 1 is assessed by 1H NMR analysis with the characteristic methylene pick at 5.54 ppm in THF-d8 (Figure 4a). Successful generation of compound 2 is assessed by 1H NMR analysis with the characteristic AB signal (&#948; = 7.73 (d, 1H, 2JH-H = 18.4 Hz, CH2), 7.30 (d, 1H, 2JH-H = 18.4 Hz, CH2) for the two inequivalent protons of the methylene in THF-d8 (Figure 4b). Successful generation of compound 3 is assessed by 1H NMR analysis in THF-d8 (Figure 4c). The most notable signals are the CHCO2 at 5.34 ppm, and the CH of the BBN fragment at 0.26 and -0.65 ppm. Successful generation of compound 4 is assessed by 1H NMR analysis in THF-d8. As shown in Figure 4d, compound 4, in situ generated from CO2, is notably characterized by a doublet at 4.64 ppm (3JH-H = 7.9 Hz, H3) and a pseudo-t at 3.36 (2JH-H = 9.7 Hz, 3JH-H = 9.5 Hz, 1H, H1b). In the isolated compound 4 from d,l-Glyceraldehyde, the four proton signals of the C3 chain are clearly observed (Figure 4e) and the three carbon atoms of the chain are characterized in the 13C{1H} NMR analysis at 76.9 (C2), 74.0(C3) and 71.5(C1) ppm (Figure 5).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/60348/60348fig1.jpg" /> 
Figure 1: Gas system. Scheme of the gas system enabling the addition of a defined pressure of CO2 at a given temperature. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60348/60348fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/60348/60348fig2a.jpg" /> 
Figure 2: Reductive functionalization of CO2. Synthesis of compounds 1 and 2. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60348/60348fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/60348/60348fig3a.jpg" /> 
Figure 3: Carbene-mediated C-C bond formation. Synthesis of compounds 3 and 4. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60348/60348fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/60348/60348fig4a.jpg" /> 
Figure 4: 1H NMR analyses of compound 1-4, recorded at room temperature in THF-d8. (A) In situ generated compound 1, (B) in situ generated compound 2, (C) isolated compound 3, (D) in situ generated compound 4 from CO2, (E) isolated compound 4 from d,l-Glyceraldehyde. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60348/60348fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/60348/60348fig5a.jpg" /> 
Figure 5: Representative characterization of compound 4 isolated from d,l-Glyceraldehyde. 13C{1H} NMR analysis recorded at room temperature in THF-d8; inlet: zoom of the C1-C3 area. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/60348/60348fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy at JoVE.com

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

CO2 transformations using a one-pot two-step method are presented herein. The purpose of the method is to give access to a variety of value-added products ...

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Nanyang Technological University

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Chemistry

7.9K Views.  Université de Toulouse, CNRS. CO2 transformations are conducted in a one-pot two-step procedure for the synthesis of complex molecules. The selective 4 e- reduction of CO2 with a hydroborane reductant affords a reactive and versatile bis(boryl)acetal intermediate which is subsequently involved in condensation reaction or carbene-mediated C-C coupling generation.

Video: Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

Retropinacol/Cross-pinacol Coupling Reactions - A Catalytic Access to 1,2-Unsymmetrical Diols

Unsymmetrical 1,2-diols are hardly accessible by reductive pinacol coupling processes. A successful execution of such a transformation is bound to a clear recognition and strict differentiation of two similar carbonyl compounds (aldehydes &#8594; secondary 1,2-diols or ketones &#8594; tertiary 1,2-diols). This fine-tuning is still a challenge and an unsolved problem for an organic chemist. There exist several reports on successful execution of this transformation but they cannot be generalized. Herein we describe a catalytic direct pinacol coupling process which proceeds via a retropinacol/cross-pinacol coupling sequence. Thus, unsymmetrical substituted 1,2-diols can be accessed with almost quantitative yields by means of an&#160;operationally simple performance under very mild conditions. Artificial techniques, such as syringe-pump techniques or delayed additions of reactants are not necessary. The procedure we describe provides a very rapid access to cross-pinacol products (1,2-diols, vicinal diols). A further extension of this new process, e.g. an enantioselective performance could provide a very useful tool for the synthesis of unsymmetrical chiral 1,2-diols.

A novel account for the synthesis of unsymmetrical 1,2-diols based on a retropinacol/cross-pinacol coupling mechanism is described. Due to the catalytic execution of this reaction a considerable improvement compared to conventional cross-pinacol couplings is achieved.

Unsymmetrical 1,2-diols are hardly accessible by reductive pinacol coupling processes. A successful execution of such a transformation is bound to a clear ...

Highly Stereoselective Synthesis of 1,6-Ketoesters Mediated by Ionic Liquids: A Three-component Reaction Enabling Rapid Access to a New Class of Low Molecular Weight Gelators

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form catalytically active N-Heterocyclic Carbenes (NHCs). Here we have used ILs as precatalysts in the addition of &#945;,&#946;-unsaturated aldehydes to chalcones to form 1,6-ketoesters, incorporating an anti-diphenyl moiety in a highly stereoselective fashion. The reaction has a broad substrate scope and several functional groups and heteroaromatics can be integrated into the ketoester backbone in generally good yields with maintained stereoselectivity. The reaction protocol is robust and scalable. The starting materials are inexpensive and the products can be obtained after simple filtration, avoiding solvent-demanding chromatography. Furthermore, the IL can be recycled up to 5 times without any loss of reactivity. Moreover, the 1,6-ketoester end product is a potent gelator in several hydrocarbon based solvents. The method enables rapid access to and evaluation of a new class of low molecular weight gelators (LMWGs) from recyclable and inexpensive starting materials.

Ionic liquids (ILs) mediate fast, simple and cheap access to 1,6-ketoesters in high diastereoselectivities and good yields. The reaction protocol is robust and the 1,6-ketoesters can be obtained in gram scale after a simple filtration protocol. Moreover, the 1,6-ketoesters are potent gelators in hydrocarbon solvents.

In organic chemistry ionic liquids (ILs) have emerged as safe and recyclable reaction solvents. In the presence of a base ILs can be deprotonated to form ...

Light-driven Enzymatic Decarboxylation

Oxidoreductases belong to the most-applied industrial enzymes. Nevertheless, they need external electrons whose supply is often costly and challenging. Recycling of the electron donors NADH or NADPH requires the use of additional enzymes and sacrificial substrates. Interestingly, several oxidoreductases accept hydrogen peroxide as electron donor. While being inexpensive, this reagent often reduces the stability of enzymes. A solution to this problem is the in situ generation of the cofactor. The continuous supply of the cofactor at low concentration drives the reaction without impairing enzyme stability. This paper demonstrates a method for the light-catalyzed in situ generation of hydrogen peroxide with the example of the heme-dependent fatty acid decarboxylase OleTJE. The fatty acid decarboxylase OleTJE was discovered due to its unique ability to produce long-chain 1-alkenes from fatty acids, a hitherto unknown enzymatic reaction. 1-alkenes are widely used additives for plasticizers and lubricants. OleTJE has been shown to accept electrons from hydrogen peroxide for the oxidative decarboxylation. While addition of hydrogen peroxide damages the enzyme and results in low yields, in situ generation of the cofactor circumvents this problem. The photobiocatalytic system shows clear advantages regarding enzyme activity and yield, resulting in a simple and efficient system for fatty acid decarboxylation.

We describe a protocol for the light-catalyzed generation of hydrogen peroxide &#8212; a cofactor for oxidative transformations.

Oxidoreductases belong to the most-applied industrial enzymes. Nevertheless, they need external electrons whose supply is often costly and challenging. ...

One-pot Microwave-assisted Conversion of Anomeric Nitrate-esters to Trichloroacetimidates

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate glycosyl donor. Following azido-nitration of a glycal, the product 2-azido-1-nitrate ester can be hydrolyzed under microwave-assisted irradiation. This transformation is usually achieved using strongly nucleophilic reagents and extended reaction times. Microwave irradiation induces hydrolysis, in the absence of reagents, with short reaction times. Following denitration, the intermediate anomeric alcohol is converted, in the same pot, to the corresponding 2-azido-1-trichloroacetimidate.

A 2-azido-1-nitrate-ester can be converted to the corresponding 2-azido-1-trichloroacetimidate in a one-pot procedure. The goal of the manuscript is to demonstrate utility of the microwave reactor in carbohydrate synthesis.

The goal of the following procedure is to provide a demonstration of the one-pot conversion of a 2-azido-1-nitrate-ester to a trichloroacetimidate ...

Biosynthesis of a Flavonol from a Flavanone by Establishing a One-pot Bienzymatic Cascade

Flavonols are a major subclass of flavonoids with a variety of biological and pharmacological activities. Here, we provide a method for the in vitro enzymatic synthesis of a flavonol. In this method, Atf3h and Atfls1, two key genes in the biosynthetic pathway of the flavonols, are cloned and overexpressed in Escherichia coli. The recombinant enzymes are purified via an affinity column and then a bienzymatic cascade is established in a specific synthetic buffer. Two flavonols are synthesized in this system as examples and determined by TLC and HPLC/LC/MS analyses. The method displays obvious advantages in the derivation of flavonols over other approaches. It is time- and labor-saving and highly cost-effective. The reaction is easy to be accurately controlled and thus scaled up for mass production. The target product can be purified easily due to the simple components in the system. However, this system is usually restricted to the production of a flavonol from a flavanone.

The derivation of a flavonol is crucial for its application in healthcare and the food industry. Here, we provide a detailed protocol for the biosynthesis of a flavonol from a flavanone and discuss the crucial steps and its advantages over other approaches.

Flavonols are a major subclass of flavonoids with a variety of biological and pharmacological activities. Here, we provide a method for the in vitro ...

Biochemistry

Utilization of Stop-flow Micro-tubing Reactors for the Development of Organic Transformations

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional batch reactors, coined stop-flow micro-tubing (SFMT) reactors. In SFMT, chemical reactions that require high pressure can be screened in parallel through a safer and convenient way. Cross-contamination, which is a common problem in reaction screening for continuous flow reactors, is avoided in SFMT. Moreover, the commercially available light-permeable micro-tubing can be incorporated into SFMT, serving as an excellent choice for light-mediated reactions due to a more effective uniform light exposure, compared to batch reactors. Overall, the SFMT reactor system is similar to continuous flow reactors and more superior than batch reactors for reactions that incorporate gas reagents and/or require light-illumination, which enables a simple but highly efficient reaction screening system. Furthermore, any successfully developed reaction in the SFMT reactor system can be conveniently translated to continuous-flow synthesis for large scale production.

A protocol for organic reaction screening using stop-flow micro-tubing (SFMT) reactors employing gaseous reactants and/or visible-light mediated reactions is presented.

A new reaction screening technology for organic synthesis was recently demonstrated by combining elements from both continuous micro-flow and conventional ...

A Two-Step Protocol for Umpolung Functionalization of Ketones Via Enolonium Species

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. Recently, we have developed a two-step strategy for ketone enolate umpolung that has enabled the development of methods for chlorination, azidation, and amination using azoles. In addition, we have developed C-C bond&#8211;forming arylation and allylation reactions. At the heart of these methods is the preparation of the intermediate and highly reactive enolonium species prior to addition of a reactive nucleophile. This strategy is thus reminiscent of the preparation and use of metal enolates in classical synthetic chemistry. This strategy allows the use of nucleophiles that would otherwise be incompatible with the strongly oxidizing hypervalent iodine reagents. In this paper we present a detailed protocol for chlorination, azidation, N-heteroarylation, arylation, and allylation. The products include motifs prevalent in medicinally active products. This article will greatly assist others in using these methods.

A two step one-pot protocol for the umpolung of ketone enolates to enolonium species and addition of a nucleophile to the &#945;-position is described. Nucleophiles include chloride, azide, azoles, allyl-silanes, and aromatic compounds.

&#945;-Functionalization of ketones via umpolung of enolates by hypervalent iodine reagents is an important concept in synthetic organic chemistry. ...

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Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for specialized equipment to achieve modest pressures, and can even be used to achieve higher pressures in more specialized equipment and sturdier reaction vessels. At the end of the reaction, the vials can be easily depressurized by opening at room temperature. In the present example CO2 serves as both a putative directing group as well as a way to passivate amine substrates, thereby preventing oxidation during the organometallic reaction. In addition to being easily added, the directing group is also removed under vacuum, obviating the need for extensive purification to remove the directing group. This strategy allows the facile &#947;-C(sp3)-H arylation of aliphatic amines and has the potential to be applied to a variety of other amine-based reactions.

Achieving Moderate Pressures in Sealed Vessels Using Dry Ice As a Solid CO2 Source

Here we present a protocol for performing reactions in simple reaction vessels under low-to-moderate pressures of CO2. The reactions can be performed in a variety of vessels simply by administering the carbon dioxide in the form of dry ice, without the need for costly or elaborate equipment or set-ups.

Herein is presented a general strategy to perform reactions under mild to moderate CO2 pressures with dry ice. This technique obviates the need for ...

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This protocol demonstrates how to use the Auto-CHO software for hierarchical and programmable one-pot synthesis of oligosaccharides. It also describes the general procedure for RRV determination&#160;experiments and one-pot glycosylation of SSEA-4.

This article presents a general experimental protocol for programmable one-pot oligosaccharide synthesis and demonstrates how to use Auto-CHO software for ...

Organocatalysis

Source: Vy M. Dong and Faben Cruz, Department of Chemistry, University of California, Irvine, CA
This experiment will demonstrate the concept of organocatalysis by illustrating the proper setup of a reaction that utilizes enamine catalysis. Organocatalysis is a form of catalysis that uses substoichiometric amounts of small organic molecules to accelerate reactions. This type of catalysis is complementary to other forms of catalysis such as transition metal or biocatalysis. Transition metal catalysis involves transition metals as catalysts and biocatalysis uses enzymes as catalysts. Some advantages of organocatalysis include the low toxicity and cost of the organocatalysts in comparison to many metal catalysts. In addition, most organocatalysts are not sensitive to air and moisture, unlike metal catalysts. In contrast to enzymes found in living organisms, the small molecules that act as organocatalysts are typically easy to access. Furthermore, organocatalysis offers complementary and new reactivity not observed with other forms of catalysis.

Versatile CO₂ Transformations into Complex Products: A One-pot Two-step Strategy

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