Stereoselective synthesis of trans-2-aryl-3-(2-pyridyl)aziridines from an α-silyl carbanion

Abstract

Five para-substituted benzaldehyde oxime O-methyl ethers (3)[Ar = phenyl, p-chlorophenyl, p-tolyl, p-methoxyphenyl, p-(N,N-dimethylamino)phenyl] reacted with 2-(trimethylsilylmethyl)pyridine (1) in the presence of lithium di-isopropylamide (LDA) in tetrahydrofuran to give the corresponding trans-2-aryl-3-(2-pyridyl)aziridines (4) in high yield (80, 85, 60, 58; and 74%, respectively), with small amounts of (Z)-1-amino-1-aryl-2-(2-pyridyl)ethenes (5), and N′,N′-di-isopropylbenzamidines (7) as by-products. The yields of compounds (4) and (5) and their ratio [(4) : (5)] were considerably influenced by experimental conditions (especially molar ratio and the addition method, of the reactants). When treated with LDA, compounds (3) were quantitatively converted into benzonitriles, which reacted, with anion (2) to give enamines (5) after elimination of a trimethylsilyl group from the corresponding N-trimeihylsilyl derivatives, or with additional LDA to give the benzamidine (7); aziridines (4) were not transformed into enamines (5) by the action of LDA. On the basis of these results, a reaction mechanism has been discussed for the formation of compounds (4).