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25.1.4.1.2 Method 2: Reduction Using Complex Aluminum Hydrides

DOI: 10.1055/sos-SD-025-00031

Harcken, C.Science of Synthesis, (20072567.

Lithium aluminum hydride and diisobutylaluminum hydride reduce carboxylic acid chlorides to the alcohols. The reagent of choice for the reduction of acid chlorides to aldehydes 4 is lithium tri-tert-butoxyaluminum hydride [LiAlH(Ot-Bu)3] (Scheme 3).[‌11‌] This reagent is commercially available or can be generated in situ from lithium aluminum hydride and 3 equivalents of tert-butyl alcohol. The reductions are performed in tetrahydrofuran or diglyme at 78°C. Under these conditions, virtually all other reducible functional groups, except aldehydes, are inert. Thus, halogens,[‌12‌‌14‌] esters (including methyl esters and acetyl protecting groups,[‌15‌,‌16‌] lactones,[‌17‌] nitriles,[‌18‌,‌19‌] and oximes[‌20‌] are not reduced under the conditions. The tricyclic acid 5 is reduced through its acid chloride 6 to the aldehyde 7 in 70% yield over two steps in the presence of its lactone and ester functionalities (Scheme 4).[‌17‌]

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