New enantioselective entry to cycloheptane amino acid polyols

摘要

A diversity-oriented protocol has been developed for the assembly of densely hydroxylated cycloheptane amino acids via succession of a vinylogous Mukaiyama aldol reaction (VMAR), a Morita-Baylis-Hillman reaction (MBHR), and an intramolecular pinacol coupling reaction (IPCR). The plan utilizes Dor L-configured glyceraldehyde derivatives as "chiral" surrogates of glyoxal and N-[(tert-butoxycarbonyl)2-(tert-butyldimethylsilyl)oxy]pyrrole as the synthetic equivalent of the alpha,gamma-dianion of gamma-aminobutanoic acid. The parallel, asymmetric syntheses of four cycloheptane representatives proceed with high diastereocontrol and virtually complete enantioselectivity in ten steps and overall yields of 15-37%.