Highly diastereoselective acetal cleavages using novel reagents prepared from organoaluminum and pentafluorophenol

Article abstract of DOI:10.1021/ja00076a030

Chiral acetals derived from aldehydes and (-)-(2R,4R)-2,4-pentanediol are cleaved selectively by organoaluminum reagents. The reaction proceeds via the retentive-alkylation process with >95% selectivities in most cases. Trialkylaluminum reagent is utilized for higher alkyl transfers, but for smaller alkyl transfers, a new reagent system, combining trialkylaluminum and the halophenols such as pentafluorophenol and 2,4,6-trichlorophenol, is employed. Chiral acetals derived from aldehydes and 1,3-butanediol are cleaved selectively by trialkylaluminum, even for smaller alkyl transfers. Oxetane is also exposed to these aluminum reagents, and the retentive-alkylation products are obtained stereoselectively. The reaction of acetals derived from (-)-(2R,4R)-2,4-pentanediol and ketones in the presence of a catalytic amount of aluminum pentafluorophenoxide produces reductively cleaved products with high diastereoselectivity. The reaction is a new means of diastereoselective cleavage of acetals: an intramolecular Meerwein-Ponndorf-Verley reductive and Oppenauer oxidative reaction on an acetal template.