DIASTEREOSELECTIVE SYNTHESIS OF 2,5-DIMETHYLPYRROLIDINES AND 2,6-DIMETHYLPIPERIDINES BY REDUCTIVE AMINATION OF 2,5-HEXANEDIONE AND 2,6-HEPTANEDIONE WITH HYDRIDE REAGENTS

The reductive amination of 2,5-hexanedione and 2,6-heptanedione with ammonia and primary amines in the presence of hydride reagents afforded 2,5-dimethylpyrrolidines and 2,6-dimethylpiperidines with variable diastereoselectivity, as the cis/trans ratio was affected by the size of the ring formed and the steric and electronic properties of the nitrogen substituent. Increasing the bulkiness of the nitrogen substituent, the cis pyrrolidines and the bans-piperidines were obtained with enhanced selectivity.