Diastereofacial selectivity in the osmylation reactions of monosubstituted alkens and conjugated E-alkenes with allylic amino aryl ketimine derivatives

Abstract

There has been considerable interest in the synthesis of optically active amino alcohols and amino acids because of their wide occurrence in biologically active molecules as well as their versatile application as chiral intermediates, auxiliaries or ligands in asymmetric synthesis. Both efficient and stereoselective construction of the vicinal amino alcohol moiety could be achieved, in principle, by controlled osmium-catalyzed dihydroxylation reactions of various chiral allylic amines that can be readily prepared from one of the chirality pools, α -amino acids. Although the diastereoselective dihydroxylation of allylic alcohols has been well established in the literature, there have been only a few systematic studies for diastereoselection in the dihydroxylation reactions of allylic amines. We report herein a systematic study on the diastereofacial selectivity of a monosubstituted olefins and conjugated E-alkenes with different allylic amino aryl ketimine derivatives. In the case of monosubstituted olefins, the common protecting groups such as N-acyl, N-alkoxycarbonyl or N,N-dibenzyl have resulted in mostly low facial selectivities except several cases. And in the case of conjugated E-system, there is only poor streoselectivities in the N-Boc series using achiral catalyst system. Tranformation of the allylic amine of monosubstituted olefins and conjugated E-alkenes into the aryl ketimine derivatives resulted in consistent higher diastereofacial selectivity in the osminum-catalyzed dihydroxylation reaction, compared to the selectivities obtained from commonly used allylic amine derivatives...