期刊
JOURNAL OF ORGANIC CHEMISTRY
卷 73, 期 12, 页码 4630-4637出版社
AMER CHEMICAL SOC
DOI: 10.1021/jo800600a
关键词
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Tertiary acyclic allyl amines and tertiary cyclic alpha-vinyl amines undergo conjugate additions to acetylenic sulfones to produce zwitterion intermediates, followed by 3-aza-Cope rearrangements. In the case of cyclic alpha-vinyl amines, the process results in ring-expansion, providing a novel route to 9- to 17-membered cyclic amines. The Hammett plot for the reaction of 8b with 2a-2f shows rho = +1.19, which is consistent with formation of the proposed zwitterion in the rate-determining step, where electron-withdrawing substituents on the arylsulfonyl moiety stabilize the negative charge and enhance the rate of the reaction. Alternative pathways were observed in methanol in the case of 11, where a methoxy substituent promotes a dissociative mechanism of the corresponding zwitterion via a stabilized allyl cation, whereas the zwitterion derived from amine 12 undergoes ring-opening by direct attack of methanol upon the strained aziridinium moiety instead of by rearrangement. An iterative process was developed, where the product of one ring-expansion is converted into a new cyclic alpha-vinyl amine, followed by a repetition of the conjugate addition and [3,3] rearrangement. This protocol was illustrated by its application to the synthesis of motuporamine A and B.
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