SYNTHESES AND REARRANGEMENTS OF SPIROCYCLIC OXAZIRIDINES DERIVED FROM UNSYMMETRICAL KETONES
SYNTHESES AND REARRANGEMENTS OF SPIROCYCLIC OXAZIRIDINES DERIVED FROM UNSYMMETRICAL KETONES
复制标题
DOI：
10.1021/jo00002a006
复制
发表时间：
1991-01-18
影响因子：
3.6
通讯作者：
TAKUSAGAWA, F
中科院分区：
文献类型：
--
作者：
AUBE, J;HAMMOND, M;TAKUSAGAWA, F
氧氮丙啶为环酮扩环提供了贝克曼重排和施密特反应的有用替代方案。 该过程包括所讨论的酮与光学活性α-甲基苄胺的缩合，所得亚胺的氧化，以及光解以提供扩环内酰胺。 光解后可以除去α-苯乙基取代基，得到N-未取代的内酰胺。 当存在远端酮取代基时，可以立体选择性地合成氧氮丙啶。 因此，通过选择光学活性α-甲基苄胺的任一对映体，可以将光学活性酮转化为任一扩环内酰胺。 具有相邻取代基的酮通常不适合这种区域控制，因为驻留取代基是氧氮杂环丙烷合成的关键立体控制元素，尽管一个值得注意的例外是2-甲氧基环己酮。 此类化合物中存在的立构中心在反应过程中发生差向异构化；此外，含有大量烯胺的底物在氧化时会产生新型双氧化产物。 最后，氧氮丙啶及其产物内酰胺中侧链的构象行为允许根据这些材料的 NMR 谱中的化学位移趋势进行一些关键的立体化学分配。
Oxaziridines provide useful alternatives to the Beckmann rearrangement and Schmidt reaction for ring enlargement of cyclic ketones. The procedure involves the condensation of the ketone in question with optically active alpha-methylbenzylamine, oxidation of the resultant imine, and photolysis to afford ring-expanded lactams. The alpha-phenylethyl substituent can be removed after photolysis to yield the N-unsubstituted lactam. When a distal ketone substituent is present, the oxaziridines can be synthesized stereoselectively. Thus, optically active ketones can be converted to either ring-expanded lactam by choice of either enantiomer of optically active alpha-methylbenzylamine. Ketones bearing adjacent substitution are generally not amenable to such regiocontrol because the resident substituent is the key stereocontrol element for the oxaziridine synthesis, although a notable exception is 2-methoxycyclohexanone. Stereogenic centers present in such compounds undergo epimerization during the couse of the reaction sequence; in addition, substrates containing substantial amounts of enamine give rise to novel doubly oxygenated products upon oxidation. Finally, the conformational behavior of the side chains in both oxaziridines and their product lactams permits some key stereochemical assignments to be made, on the basis of chemical shift trends in the NMR spectra of these materials.