hide
Free keywords:
(S)-PROLINE BENZYL ESTER; CHIRAL AUXILIARIES; AQUEOUS-SOLUTION; CYCLOCONDENSATION REACTION; CYCLOADDITIONS; PIPERIDINE; ALKALOIDS; SCOPE
Abstract:
Imines 1 obtained from aromatic, aliphatic or functionalized aldehydes and valine tert-butyl ester undergo Lewis acid catalyzed hetero Diels-Alder reactions with Brassard's diene 2. The cycloadducts are formed in good to high yields and with diastereomer ratios of 92:8-97:3. For the removal of the chiral auxiliary group a new method was developed whose principle consists in the conversion of the amino acid alpha-C-atom into an acetalic center employing a Curtius rearrangement as the key step.
