Asymmetric addition of 2-methylfuran and its lithiated derivative to variously N, N-protected l-alaninals

Abstract

The asymmetric reaction of 2-methylfuran 2a and its lithiated derivative 2b with N, N-diprotected l-alaninals 1a– c, carried out under high pressure conditions in the presence of Lewis acid-catalyst, are described. For aldehyde 1a two diastereoisomeric adducts anti- 3a and syn- 3a were formed, with predominance of the former. In the case of aldehydes 1b and 1c only the anti-diastereoisomers 3b or 3c were formed, but accompanied by two diastereoisomeric oxazolidinones trans- 4 and cis- 4. The absolute configuration (via X-ray analysis of anti- 5 and chemical correlations) and the extent of asymmetric induction were established.