All articles of this category Aldimines of 2,3,4,6-tetra- 0 -pivaloyl- β -D-galactosylamine react with 1-methoxy-3-trimethylsilyloxybuta-1,3-diene in a Mannich-Michael condensation reaction sequence to give 2-substituted N -galactosyl-5,6-dehydropiperidin-4-ones 3 with high diastereoselectivity. The X-ray analysis of the 2-propyl derivative 3a proved ( R )-configuration of the major diastereomer and led to the correction of our earlier assignment of configuration for (-)-coniine hydrochloride 9a obtained from this intermediate. Despite their low reactivity, these enaminones 3 can be converted into chiral 2,6- cis -disubstituted piperidinones 12 with high stereoselectivity by reaction with organocuprates in combination with hard electrophiles. Enantiomerically pure alkaloids such as (-)-dihydropinidine and gephyrotoxine 167B have been synthesized according to this methodology. asymmetric synthesis - tandem Mannich-Michael reaction - 1,4 addition to enaminones - piperidine alkaloids - configuration of ( R )-coniine
No takes yet. Share an insight, caveat, or question.
Weymann et al. (1997) studied this question.