The preparation of the strained cis-2,3-di-tert-butylcyclopropanone 2 from the acyclic compound, α,α′-dibromodineopentyl ketone 1, using a previously reported methodology, is dramatic evidence of both the existence of oxyallyl intermediates in the mechanism of this reaction, and of the integrity with which oxyallyls ring-close to cyclopropanones by a disrotatory route. Because of the bulky cis substituents, cyclopropanone 2 exhibits a number of unusual spectroscopic features (as compared to the trans isomer 5). With the aid of ab initio calculations on 2 and 5, it can be shown that the C2—C3 bond in 2 interacts with the carbonyl π-orbitals, thus causing the carbonyl oxygen to bend 12° out of the plane; this interaction is absent in 5 and the latter has a planar carbonyl group. As with other cyclopropanones, 2 can be photochemically decarbonylated. This process itself appears to be stereospecific even though highly strained alkenes are produced. Cyclopropanone 2 is thermally rearranged to the trans isomer 5 and the kinetics for this are reported; our favoured mechanism involves oxyallyl intermediates. Other reactions of 2 also appear to proceed through these oxyallyl species; for example, alcohols initially add to 2 to give α-alkoxy ends, solutions of 2 enter into very facile diene cycloadditions, and the dimerization of neat 2 also appears to involve these oxyallyl species. Keywords: cyclopropanones, oxyallyl, stereomutation, stereospecific decarbonylation, nonplanar carbonyl.
从无环化合物α,α'-二溴二新戊酮1,使用先前报道的方法制备高度应变的顺式2,3-二叔丁基环丙酮2,是这种反应中氧丙烯中间体存在以及氧丙烯通过反转路径环闭合成环丙酮的完整性的戏剧性证据。由于体积庞大的顺式取代基,与反式异构体5相比,环丙酮2表现出许多不寻常的光谱特征。通过对2和5的从头计算,可以显示2中的C2-C3键与羰基π轨道相互作用,从而导致羰基氧向外弯曲12°; 在5中不存在这种相互作用,后者具有平面的羰基基团。与其他环丙酮一样,2可以光化学脱羰作用。即使产生高度应变的烯烃,该过程本身似乎也是立体特异性的。环丙酮2被热重排为反式异构体5,报道了这个过程的动力学; 我们喜欢的机制涉及氧丙烯中间体。2的其他反应似乎也通过这些氧丙烯物种进行; 例如,醇最初添加到2中以给出α-烷氧末端,2的溶液进入非常容易的二烯基环加成反应,而无水2的二聚似乎也涉及这些氧丙烯物种。关键词:环丙酮,氧丙烯,立体异构,立体特异性脱羰作用,非平面羰基。