BOUVEAULT-BLANC REDUCTION PDF

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A new sodium dispersion reagent has been evaluated for the reduction of esters. The method compares favorably with modern metal hydride reductions and is much safer and efficient than the traditional Bouveault—Blanc reduction. Scheme a Conditions: 1 0. Scheme e Conditions: Na-D15 6. Conditions: 1 0. Conditions: Na-D15 6. Results reported in ref 1d. The American Chemical Society holds a copyright ownership interest in any copyrightable Supporting Information.

Files available from the ACS website may be downloaded for personal use only. Users are not otherwise permitted to reproduce, republish, redistribute, or sell any Supporting Information from the ACS website, either in whole or in part, in either machine-readable form or any other form without permission from the American Chemical Society. For permission to reproduce, republish and redistribute this material, requesters must process their own requests via the RightsLink permission system.

We thank Pentagon Fine Chemicals Ltd. For a detailed discussion of alkali metal anions stabilized by crown ethers for potential applications in functional group reductions, see:. For other recent methods for the reduction of carboxylic acid derivatives, see:. It is noteworthy that most commonly used metal hydrides are directly or indirectly made from sodium metal:. Sodium dispersion Na-D15 is commercially available. Please see the Supporting Information for the details of the commercial supplier.

When toluene was used as solvent, it is possible that the reduction of esters was promoted by the arene radical formed by electron transfer from sodium to toluene. For large-scale reactions, it is more convenient to transfer a solution of ester substrate and i -PrOH in hexane to Na-D View Author Information.

Cite this: J. Article Views Altmetric -. Citations PDF KB. Abstract High Resolution Image. The dissolving metal reduction of esters has found widespread use in synthesis for access to important alcohols. To facilitate this process, the sodium lump is normally precut into small pieces. Herein, we present the use of a pre-prepared, nonpyrophoric, and high surface area sodium dispersion, Na-D15, in place of sodium lump for the Bouveault—Blanc reduction.

To our knowledge, no systematic study of the application of a pre-prepared sodium dispersion for the electron transfer reductions of esters has been reported. Scheme 1. High Resolution Image. The sodium dispersion Na-D15 Scheme 1 B is prepared by a robust, reliable, and scalable sodium dispersion technology.

Na-D15 is transferable by syringe or pipette and can easily be handled in the open atmosphere, thus its use offers key advantages over that of alternative sodium dispersions. The feasibility of using Na-D15 as a base in large-scale industry synthesis has already been demonstrated. The low yield was due to the competitive oxidation of sodium by EtOH. Table 1. Given the fast side reaction between Na-D15 and the protic solvent and the poor miscibility of the suspending agent in Na-D15 in alcohols, the application of other aprotic solvents was explored.

EtOH could be replaced by other proton sources, and i -PrOH was found to be the most effective alcohol whose use led to a quantitative yield of 2a entry 8, Table 1. When H 2 O was used instead of an alcohol, intermolecular acyloin condensation gave rise to the major product, most likely due to the poor miscibility of H 2 O in hexane. Following the optimization studies, the influence of the ester group was investigated using a range of esters derived from hydrocinnamic acid.

Methyl, ethyl, isopropyl, n -butyl, phenyl, and 2-methoxyethyl esters were all reduced in high yield Table 2. More hindered ester 1c was reduced in a slightly lower yield entry 3, Table 2.

Similarly, allyl and benzyl esters were also reduced to the corresponding alcohols in high yields entries 5 and 6, Table 2. Table 2. Reduction of Hydrocinnamic Esters with Na-D15 a. The scope of this reduction was then investigated using a range of aliphatic ester and lactone substrates. The results demonstrate that a broad range of esters readily participate in the reaction Scheme 2. Primary, secondary, and tertiary alkyl esters were all reduced to the corresponding primary alcohols in excellent yields.

Minimal impact on the yield was observed with sterically hindered substituents 1l and 1o , Scheme 2. A substrate with an acidic proton was also tolerated very well 1n , Scheme 2. The substrates bearing both internal and terminal olefins 1q and 1r , Scheme 2 were reduced smoothly to the corresponding alcohols. Furthermore, this protocol tolerates the heterocyclic ring in ester 1j and is able to reduce lactone 1m to the corresponding diol.

Importantly, no significant change in yields has been observed upon scale up of this reaction from 0. Scheme 2. Reduction of Esters with Na-D15 a , b. Table 3 shows further examples of functional group tolerance. It is noteworthy that aryl fluorides are not tolerated in the improved Bouveault—Blanc reduction using Na-SG I stage I sodium in silica gel. However, chloride on an aromatic ring was fully reduced when 6. Table 3. Next, the reduction of esters using deuterated alcohols was conducted Scheme 3.

The formation of 2 -D,D compounds suggests that anions are generated and protonated by the alcohol during a series of single electron transfers. The kinetic isotope effect was determined as shown in Table 4. The results suggest that, when EtOH and i -PrOH were used as the proton donor, the proton transfer is not involved in the rate-determining step for the reduction of simple and sterically demanding esters.

Table 4. Determination of Primary Kinetic Isotope Effect. Table 5. Only 4. A broad range of aliphatic esters was reduced in high yields under mild conditions without external heating. The base-promoted side reactions observed in traditional Bouveault—Blanc reductions were suppressed by using Na-D15, and higher yields were obtained. The chemoselectivity of Na-D15 has been demonstrated to be comparable with metal hydrides.

Given that Na-D15 is easy to handle and stable, this protocol provides an attractive alternative to the use of pyrophoric metal hydrides for ester reduction.

Experimental Section. Glassware was dried in an oven overnight before use. NMR data were collected at either or MHz. All samples were analyzed in CDCl 3 unless otherwise stated. All compounds used in this study have been described in the literature 1 or are commercially available.

All solvents and reagents were used as supplied. Esters were purchased from commercial suppliers or prepared by standard methods. To a solution of ester 0. After the specified time typically 0—10 min , the reaction was quenched by an aqueous solution of HCl 1.

According to the general procedure, the reaction of methyl 3-phenylpropanoate 0. According to the general procedure, the reaction of ethyl 3-phenylpropanoate 0. Spectroscopic properties matched those previously described. According to the general procedure, the reaction of isopropyl 3-phenylpropanoate 0.

According to the general procedure, the reaction of butyl 3-phenylpropanoate 0. According to the general procedure, the reaction of allyl 3-phenylpropanoate 0.

According to the general procedure, the reaction of benzyl 3-phenylpropanoate 0. According to the general procedure, the reaction of phenyl 3-phenylpropanoate 0. According to the general procedure, the reaction of 2-methoxyethyl 3-phenylpropanoate 0. Na-D15 A solution of methyl 3-phenylpropanoate After 5 min, the reaction was quenched by an aqueous solution of HCl 50 mL, 3.

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Bouveault–Blanc reduction

Sodium dispersions are used as the electron donor in this electron transfer reaction, and ethanol-d 1 is employed as the deuterium source. This reaction uses stable, cheap, and commercially available reagents, is operationally simple, and results in excellent deuterium incorporation across a broad range of aliphatic esters, which provides an attractive alternative to reactions mediated by expensive pyrophoric alkali metal deuterides. This site needs JavaScript to work properly. Please enable it to take advantage of the complete set of features! Clipboard, Search History, and several other advanced features are temporarily unavailable. Search: Search. Advanced Clipboard.

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File:Bouveault-Blanc Reduction Mechanism.png

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Bouveault-Blanc Reduction

Description: Reaction mechanism of the Bouveault-Blanc reduction. This file contains additional information such as Exif metadata which may have been added by the digital camera, scanner, or software program used to create or digitize it. If the file has been modified from its original state, some details such as the timestamp may not fully reflect those of the original file. The timestamp is only as accurate as the clock in the camera, and it may be completely wrong. From Wikimedia Commons, the free media repository. File information. Structured data.

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