Aziridination of β-substituted styrene derivatives with 3-acetoxyaminoquinazolin-4(3H)-ones: probing transition state geometry from changes in diastereoselectivity

摘要

Reaction of (S)-3-acetoxyamino-2-[1-(t-butyldimethylsilyloxy)ethyl]quinazolin-4(3H)-one 5 (Q1nNHOAc)nwith styrene and R(β)-substituted E-styrenes (R = SiMe3, Me, CH2Cl, CHCl2) gives the correspondingnaziridines diastereoselectively. The diastereoselectivity increases in the same sense from 5 : 1 20 : 1 as thenelectron-withdrawing character of R increases [H(Me), CH2Cl, CHCl2] but is accompanied by a decrease innyield of aziridine. A similar increase in diastereoselectivity is found in the reaction of 3-acetoxyamino-n2-(2,3,3-trimethylpropyl)quinazolin-4(3H)-one 38 (Q4nNHOAc) with the same β-substituted styrenes.nAn explanation for these observations is offered based on a tighter, more symmetrical transition statenfor the aziridination of styrenes bearing the more electron-withdrawing β-substituents and is supported bynSCF calculations.