Alane aromatic aldehydes

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. 

Alane (AIH3) and its derivatives have also been utilized in the reduction of carboxylic acids to primary alcohols. It rapidly reduces aldehydes, ketones, acid chlorides, lactones, esters, carboxylic acids and salts, tertiary amides, nitriles and epoxides. In contrast, nitro compounds and alkenes are slow to react. AIH3 is particularly useful for the chemoselective reduction of carboxylic acids containing halogen or nitro substituents, to produce the corresponding primary alcohols. DIBAL-H reduces aliphatic or aromatic carboxylic acids to produce either aldehydes (-75 °C) or primary alcohols (25 C) Aminoalu-minum hydrides are less reactive reagents and are superior for aldehyde synthesis. ... 

Aromatic and aliphatic A,iV-dialkyl carboxylic acid amides, carboxylic esters, and free carboxylic acids are converted into aldehydes by diisobutyl-alane if reduction is carried out at low temperatures (0°C or — 70°C) 269, 279, 280, 286) ... 

At elevated temperatures 2 moles of dialkyl alane react with nitriles up to the amine stage. The dialkyl-dialkylamino alanes, R NR fCHaR"), resulting from azomethines form molecular compounds with strong donors. These are colored if the donor is an azomethine or an aromatic N heterocycle and may be used for the quantitative determination of A1H groups in organic aluminum compounds 191). Complex salts such as Li[(RO)jAlH] 37, 38) or Na iC s AlIR] 287) may be used in the preparation of aldehydes instead of diisobutylalane (cf. Section V,D,3b). 

---