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Addition of Organozincate Reagents to Imines Derived from ( S )‐1‐Phenylethylamine and Ethyl ( S )‐Valinate—Synthesis of ( S )‐1‐(2‐Pyridyl)Alkylamines
Author(s) -
Alvaro Giuseppe,
Pacioni Paolo,
Savoia Diego
Publication year - 1997
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.19970030512
Subject(s) - chemistry , imine , reagent , aldimine , boron trifluoride , aryl , medicinal chemistry , alkyl , pyridine , chiral auxiliary , organic chemistry , catalysis , enantioselective synthesis
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 diastereoselectivies. 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 3 and underwent selective group transfer from mixed zincates at — 78°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.