Alkenyl Fischer carbene complexes and alpha,beta-unsaturated imine derivatives: Synthesis of azepines and mechanistic NMR studies
Alkenyl Fischer carbene complexes and alpha,beta-unsaturated imine derivatives: Synthesis of azepines and mechanistic NMR studies
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DOI：
10.1002/chem.19960020116
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发表时间：
1996-01-01
影响因子：
4.3
通讯作者：
Pertierra, P
中科院分区：
文献类型：
--
作者：
Barluenga, J;Tomas, M;Pertierra, P
4-氨基-1-氮杂二烯1与α，β-不饱和Fischer卡宾络合物在-40℃下反应，立体选择性地得到各种取代的~3H-4，5-二氢氮杂二烯3；类似地，1-羟基-1-氮二烯(α，β-不饱和肟类)6得到相应的氮杂环丙烷衍生物7。手性非外消旋卡宾络合物11得到氮杂卓12-13(D.E.=40-44%)；结晶后，主要异构体以非对映异构体和对映体纯的形式获得(总收率45-50%)。12A的X射线结构允许绝对立体化学的归属。合成的氮杂环己烷的酸解得到了外消旋和对映体纯的1，6-二羰基化合物(+/-)-5，(+/-)-9和(-)-14，以及二醇(-)-15。通过四个中间体(A、B、C和D)的低温多核(H-1、C-13、N-15和W-183)核磁共振表征，研究了1和2的反应机理。实验过程包括：i)1，2-未取代亚胺氮与金属卡宾功能(两性离子A，-60℃)的1，2-亲核加成，ii)环化到七元环上，并有五个羰基金属的1，2-迁移(两性离子B，-40℃)，iii)金属还原消除和配位到胺氮(中间体C，-40℃)，以及iv)热分解和互变异构化(中间体D和化合物3，在-20℃以上)。
4-Amino-1-azadienes 1 react with alpha,beta-unsaturated Fischer carbene complexes at -40 degrees C to give stereoselectively a variety of substituted 3H-4,5-di-hydroazepines 3; similarly, 1-hydroxy-1-azadienes (alpha,beta-unsaturated oximes) 6 afforded the corresponding azepine derivatives 7. Chiral, nonracemic carbene complexes 11 gave azepines 12-13 (d.e. = 40-44%) upon reaction with oxime 6a; the major isomers were obtained in a diastereomerically and enantiomerically pure form (45-50% overall yield) after crystallization. An X-ray structure of 12a allowed assignment of the absolute stereochemistry. The acid hydrolysis of azepines synthesized provided racemic and enantiomerically pure 1,6-dicarbonyl compounds (+/-)-5, (+/-)-9, and (-)-14, as well as diol(-)-15. The mechanism of the reaction of 1 and 2 was investigated by multinuclear (H-1,C-13, N-15, and W-183) NMR characterization of four intermediates (A, B, C, and D) at low temperature. The experimental sequence of events involves: i) 1,2-nucleophilic addition of the unsubstituted imine nitrogen of 1 to the metal carbene function (zwitterion A, -60 degrees C), ii) cyclization to the seven-membered ring with 1,2-migration of the pentacarbonyl metal (zwitterion B, -40 degrees C), iii) reductive elimination and coordination of the metal to the amine nitrogen (intermediate C, -40 degrees C), and iv) thermal decomplexation and tautomerization (intermediate D and compound 3, above - 20 degrees C).