Tetrabutylammonium borohydride aldehydes

The reducing power of tetralkylammonium borohydrides in dichloromethane is similar to that observed in water or alcohol. A convenient preparation of tetrabutyl-ammonium borohydride has recently been reported [11] and the utility of the reagent has been surveyed [12]. In dichloromethane solution, tetrabutylammonium borohydride readily reduces aldehydes, ketones and acid chlorides while reacting only very slowly with esters (see Table 12.2). 

Chemical reduction of aromatic aldehydes to alcohols was accomplished with lithium aluminum hydride [5i], alane [770], lithium borohydride [750], sodium borohydride [757], sodium trimethoxyborohydride [99], tetrabutylam-monium borohydride [777], tetrabutylammonium cyanoborohydride [757], B-3-pinanyl-9-borabicyclo[3.3.1]nonane [709], tributylstannane [756], diphenylstan-nane [114], sodium dithionite [262], isopropyl alcohol [755], formaldehyde (crossed Cannizzaro reaction) [i7i] and others. 

Crossed aldol reaction between an aromatic aldehyde and the TMS enolate of another aldehyde proceeds smoothly in wet or dry DMF using a lithium carboxylate as Lewis base catalyst.158 One-pot conversion to 1,3-diols using sodium borohydride as reductant gives up to 87% yield. A similar report, using tetrabutylammonium phe-nolates as Lewis bases, is diaslereoselective.159... 

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