Tandem [1,5]-H shift/6蟺-electrocyclizations of ketenimines bearing 1,3-oxathiane units. Computational assessment of the experimental diastereoselection

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• 作者：Mateo Alajarin^a ; Baltasar Bonillo^a ; Marta Marin-Luna^a ; Pilar Sanchez-Andrada^b ; ^{pilar.sanchez@cud.upct.es} ; Angel Vidal^a ; ^vidal@um.es ; Raul-Angel Orenes^c
• 关键词：1 ; 3-Oxathiane ; Ketenimine ; Hydride migration ; electrocyclization ; DFT study
• 刊名：Tetrahedron
• 出版年：2012
• 期刊代码：107_00404020
• 类别：ch
• 出版时间：17 June, 2012
• 卷：68
• 期：24
• 页码：4672-4681
• 文件大小：1184 K

摘要

N-Aryl ketenimines bearing a 1,3-oxathiane function at the ortho position of the keteniminic nitrogen atom convert into spiro[1,3-oxathiane-2,4鈥?3鈥?em>H)quinolines] under mild thermal treatment. These cyclization processes are interpreted in terms of a two-step tandem sequence involving a [1,5]-H migration followed by a 6蟺-electrocyclic ring closure. Moreover, the cyclization of 1,3-oxathiane-ketenimines having two different substituents at the terminal carbon atom of the ketenimine moiety provided spiroquinolines bearing two stereocenters, the C3 and C4 atoms, with moderate diastereoselectivity. A DFT study support that the mechanism of these conversions consists of a [1,5]-H shift/6蟺-electrocyclization sequence, in which the [1,5]-H shift is the rate-limiting step. A quantitative kinetic analysis of the cyclization of an oxathiane-ketenimine with a prochiral ketenimine function explains the sense and degree of the experimentally observed diastereoselectivity.