Regio- and stereoselective conjugate addition of nitrogen nucleophiles to 2-alkenyl n-methylthiazolium iodides. synthesis of d-3-epi-daunosamine and some lincosamine analogs

A two-carbon homologation-amination technology of aldehydes is described. Key steps involve the Michael-type addition of a nitrogen nucleophile (benzylamine, trimethylsilylazide, potassium phtalimide) to a 2-alkenyl N-methylthiazolium salt obtained by olefination of the aldehyde with the phosphorane (1), and the thiazole-to-formyl deblocking. The addition of benzylaminine to the thiazolium salt derived from the acetonide of D- glyceraldehyde occurs with a good level of syn-diastereoselectivity (ds, 85-90 %) in agreement with a modified Felkin-Anh model. This technology is employed in short synthetic routes to D-3-epi-daunosamine from 4-deoxy D-threose and some lincosamine analogues from α-D-dialdogalactopyranose. © 1990.