SELECTIVE REDUCTION OF ACYL CHLORIDES TO ALDEHYDES BY ANIONIC-6B TRANSITION-METAL HYDRIDES
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Acyl chlorides can be selectively and rapidly reduced, under mild conditions, by group 6B anionic hydrides, HM(CO)4L- (M = Cr, W; L = CO, PR3), giving the corresponding aldehydes and the metal chlorides CIM-(CO)4L-. The reaction is nearly quantitative for both aliphatic and aromatic acyl chlorides using solvent systems such as dichloromethane, tetrahydrofuran, or acetonitrile. Only in the presence of acid will the aldehydes consume a second equivalent of hydride, subsequently being reduced to alcohols. The anionic hydrides selectively reduce acyl chlorides in the presence of other reducible groups such as alkyl bromides or nitro aromatics. In situ preexchange of hydrogen by deuterium (HM(CO)4L-/CH3OD DM(CO)4L-/CH3OH) allows for deuterium delivery, giving RCDO products, as indicated by 2H NMR. 1984, American Chemical Society. All rights reserved.