Reduction using borohydrides

In this case, the metal is fixed to the membrane either by chemical reduction using borohydride or by calcination of the membrane at temperatures of 175-200°C. Using the latter method, the catalyst is less sensitive to be washed out during the hydrogenation reaction. 

Despite their availability and practical utility, examples of iron-catalysed olefin reductions using borohydride reagents are quite limited. Both Ashby and Boger reported the use of either stoichiometric or superstoichiometric quantities of iron in combination with borohydride reagents for olefin hydrogenation (see Section 12.6.2). ... 

Macrocycles have been prepared by formation of macrocyclic imines as well as by using variations of the Williamson ether synthesis ". Typically, a diamine or dialdehyde is treated with its counterpart to yield the Schiff s base. The saturated macrocycle may then be obtained by simple reduction, using sodium borohydride, for example. The cyclization may be metal-ion templated. In the special case of the all-nitrogen macrd-cycle, 15, the condensation of diamine with glyoxal shown in Eq. (4.14), was unsuccess-ful ... 

When the furanones 110 (R = Ph, p-MeOC6H4, p-Cl—C6H4) were subjected to reduction using sodium borohydride, neither the glycols 111 nor the allyl alcohols 112 were formed. Instead, the corresponding 4-(arylmethylene)-2,3-(4//,5// )-furandiones 113 were obtained (Scheme 34) (86JHC199). 

Fenticonazole (106), on the other hand, is used topically to combat a wide variety of dermatophytes and yeasts, particularly Candida albicans. It can be synthesized from 2,4-dichlo-rophenacyl chloride (104) by reduction with borohydride and subsequent displacement with imidazole to give 105. This last undergoes ether formation with p-thiolphenylbenzyl chloride mediated by NaH to produce fcnticonazole (106) [37]. 

Two ring reductions using sodium borohydride were reported. The reduced derivative 157 underwent further reduction in the six-membered ring with methanolic sodium borohydride under heating for 15 min to give the... 

Chaplin used methanolysis for the analysis of carbohydrates in glycoproteins. His method was a variation of the foregoing procedures, with an improvement of using tert-hvAyX alcohol to remove hydrogen chloride by coevaporation, instead of prolonged trituration with silver carbonate. His method is useful for samples containing uronic acids and lipids. Mononen studied methanolysis, followed by deamination and reduction with borohydride, for determination of the monosaccharide constituents of glycoconjugates. This method was applied to a lipid-free, protein fraction of rat brain. 

In the reductions with borohydrides and boranes the isolation of products differs from that used in the reductions with lithium aluminum hydride, the... 

The ylide 140 <2000JOC8068> is stable to attempted reduction using sodium borohydride, diisobutylaluminium hydride (DIBAL-H), or lithium aluminium hydride <2000JOC6388>, but eliminates propene on heating to form the annulated parent 141. Oxidation of the latter with lead(iv) oxide and potassium carbonate forms a radical, 142, which is stable to chromatography and can be stored in air for several days. 

Among the various other syntheses achieved by mild chemical routes, mention must be made of the synthesis of hydrides of metals and alloys using borohydride reduction in aqueous medium (Murphy et al, 1993). The reaction seems to proceed as follows ... 

A study of the influence of the nature of the solid support showed that silica, celite, cellulose or magnesium sulphate in combination with borohydride can also be used successfully in the microwave-assisted reduction of carbonyl compounds. The choice of the solid support has been reported to influence the chemoselectivity of the reduction of chalcone. Under optimised conditions the reduction of the alkene can be suppressed using borohydride on silica, whereas the use of cellulose as solid support seems to favour C=C reduction (Scheme 4.11 )27. 

The Cannizzaro reaction, that is, the base-catalysed disproportionation of a carbonyl compound to an alcohol and a carboxylic acid, has gained some importance as an economically viable alternative to the reduction with borohydrides. However, the reaction is restricted to carbonyl compounds without any a-hydrogen, which do not undergo competing aldol reactions. Thus, mainly aromatic aldehydes are used for this kind of transformation. The protocols developed for microwave applications typically involve solvent-free conditions using alumina as the solid support. Under these conditions, a significant acceleration of the reaction was achieved. 

Reduction by LiAlH4 of 2,3-dihydrothieno[3,2-6]thiophen-3-one (22) and its 2-methyl- and 2-ethyl-derivatives afforded the appropriate thienothiophene 2.21,25,28,29 Similarly, Gronowitz and co-workers48 used borohydride reduction of ketones 33 and 34 to prepare 2-methyl-thieno[3,2-6]thiophene (35). Attempts to reduce 2,3-dihydrothieno[3,2-6]thiophen-3-one (22)28 and 2,3-dihydro-4,6-dimethylthieno[3,4-6]-thiophen-3-one (87)T with zinc powder in acetic acid were unsuccessful. 

A review describing the major advances in the field of asymmetric reduction of achiral ketones using borohydrides, exemplified by oxazaborolidines and /9-chlorodiisopino- camphenylborane, has appeared. Use of sodium borohydride in combination with chiral Lewis acids has been discussed.298 The usefulness of sodium triacetoxyboro-hydride in the reductive amination of aldehydes and ketones has been reviewed. The wide scope of the reagent, its diverse and numerous applications, and high tolerance for many functional groups have been discussed.299 The preparation, properties, and synthetic application of lithium aminoborohydrides (LABs) have been reviewed. 

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