Reaction of (S)-3-acetoxyamino-2-[1-(t-butyldimethylsilyloxy)ethyl]quinazolin-4(3H)-one 5 (Q1NHOAc) with styrene and R(β)-substituted E-styrenes (R = SiMe3, Me, CH2Cl, CHCl2) gives the corresponding aziridines diastereoselectively. The diastereoselectivity increases in the same sense from 5 â¶ 1 â 20 â¶ 1 as the electron-withdrawing character of R increases [H(Me), CH2Cl, CHCl2] but is accompanied by a decrease in yield of aziridine. A similar increase in diastereoselectivity is found in the reaction of 3-acetoxyamino-2-(2,3,3-trimethylpropyl)quinazolin-4(3H)-one 38 (Q4NHOAc) with the same β-substituted styrenes.An explanation for these observations is offered based on a tighter, more symmetrical transition state for
the aziridination of styrenes bearing the more electron-withdrawing β-substituents and is supported by SCF calculations.
(S)-3-乙酰氧胺基-2-[1-(叔丁基二甲基
硅氧基)乙基]
喹唑啉-4(3H)-酮5 (Q1NHOAc)与
苯乙烯及R(β)-取代的E-
苯乙烯(R = SiMe3, Me,
CH2Cl,
CHCl2)的反应,可选择性地生成相应的
氮丙啶。随着R的吸电子特性增强[H(Me), , ],立体选择性从5:1增加到20:1,但
氮丙啶的产率却降低。3-乙酰氧胺基-2-(2,3,3-三甲基丙基)
喹唑啉-4(3H)-酮38 (Q4NHOAc)与相同的β-取代
苯乙烯反应,也观察到类似的立体选择性增加。这些现象的解释基于更紧密、更对称的过渡态,用于带有更强吸电子β-取代基的
苯乙烯的
氮丙啶化,并通过SCF计算得到支持。