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Influence of HMPA on the Stereochemical Outcome of the Addition of a Racemic Allenylzinc onto Enantiopure N‐ tert ‐Butanesulfinimines: Stereoselective Access to Enantiopure cis ‐Ethynylaziridines
Author(s) -
Ferreira Franck,
Audouin Max,
Chemla Fabrice
Publication year - 2005
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.200500268
Subject(s) - enantiopure drug , stereoselectivity , chemistry , selectivity , kinetic resolution , stereoisomerism , stereochemistry , medicinal chemistry , enantioselective synthesis , organic chemistry , molecule , catalysis
In the presence of 60 equivalents of HMPA, the condensation of the racemic allenylzinc derived from 1‐chloro‐3‐trimethylsilylpropyne onto enantiopure non‐α‐branched N‐ tert ‐butanesulfinimines was proven to give access to the corresponding cis ‐ethynylaziridines as the major products. The good cis selectivity observed presumably resulted from a high kinetic resolution with the allenylzinc being partially configurationally labile with respect to the time scale defined by the rate of the reaction. Both single crystal X‐ray analysis and semiempirical calculations conducted at the MM2 and AM1 levels of theory proved that the reaction certainly occurred through a preferred synclinal transition state in a supra‐ or antarafacial S E 2′ process. In all cases, chromatographic purification over silica gel allowed the cis ‐ethynyl‐N‐ tert ‐butanesulfinylaziridines to be obtained as diastereo‐ and enantiomerically pure compounds ( dr >98:2 and ee >99 %).