Addition of organozincate reagents to imines derived from (S)-1-phenylethylamine and ethyl (S)-valinate - Synthesis of (S)-1-(2-pyridyl)alkylamines

Triorganozincates were added to aliphatic aldimines derived from (S)-1-phenylethylamine and (S)-valine esters in the presence of boron trifluoride to give secondary amines with low diastcreoselectivies, From mixed zincates, most alkyl groups (methyl, ethyl, 1-heptynyl, but not tert-butyl) could be transferred. No addition to benzaldimines was observed, but the imines prepared from 2-pyridinecarboxaldehyde did not require activation by BF, and underwent selective group transfer from nw;ed zincates al -78 degrees C. Excellent diastereoselectivities were observed in the reactions of the 2-pyridine imine derived from ethyl (S)-valinate with mixed zincates, in which the methyl group was used as nontransferable ligand, allowing the transfer of alkyl and vinyl groups with excellent to complete selectivity. However, dimethyl(aryl)- and dimethyl-(1-heptynyl)zincates did not react. (S)-1(2-Pyridyl)alkylamines were prepared with high optical purity by subsequent removal of the chiral auxiliary.