Asymmetric synthesis of (+) and (-) trans-2,6-dimethylpiperidines

Article abstract of DOI:10.1016/S0040-4020(97)00525-5

(+) aid (-) trans-2,6-dimethylpiperidines 9 have been prepared from diastereomeric lactams 6 and 11, both available from (R)-(-)-phenylglycinol 4. Diastereoselective C-2 alkylation afforded oxazolidines 7 and 12. Reduction of 7 with LiAlH₄ or NaBH₄ led to trans-2,6-8 with total retention of configuration. When 12 was reduced with NaBH₄, trans derivative 13a was isolated as the major isomer. A mechanism is proposed to explain the different results.