Bu3SnH-mediated pinacol coupling of 1,5- and 1,6-dicarbonyl compounds:: Synthetic and mechanistic studies
Bu3SnH-mediated pinacol coupling of 1,5- and 1,6-dicarbonyl compounds:: Synthetic and mechanistic studies
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DOI：
10.1021/jo9809130
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发表时间：
1998-09-04
影响因子：
3.6
通讯作者：
Fu, GC
中科院分区：
文献类型：
--
作者：
Hays, DS;Fu, GC
采用Bu3SnH作为化学计量还原剂，描述了1,5-和1,6-二羰基化合物分子内蒎醇偶联的新方法。蒎醇环化的关键步骤是在羰基上加入锡基和随后的分子内S(H)2反应。1,3-二氧二甲酸-2-锡烷的分离，以及其他产物和标记研究，为所提出的均溶取代步骤提供了强有力的支持，该步骤将品纳醇环化与锡酮的其他还原环化区分开来，所有这些环化都是在最后一步从Bu3SnH中提取氢。S(H)2途径的一个有趣结果是1,5-二羰基化合物的环化具有很高的顺式选择性。机理研究证明，均溶取代之前的步骤，包括C-C键的形成，在反应条件下是可逆的。
A new method is described for the intramolecular pinacol coupling of 1,5- and 1,6-dicarbonyl compounds, employing Bu3SnH as the stoichiometric reductant. The key steps in this pinacol cyclization are the addition of a tin ketyl to a carbonyl group and a subsequent intramolecular S(H)2 reaction. The isolation of 1,3-dioxa-2-stannolanes, along with other product and labeling studies, provides strong support for the proposed homolytic substitution step, which distinguishes the pinacol cyclization from other reductive cyclizations of tin ketyls, all of which proceed through abstraction of hydrogen from Bu3SnH in the final step. An interesting consequence of the S(H)2 pathway is very high cis selectivity in the cyclization of 1,5-dicarbonyl compounds. Mechanistic studies furnish evidence that the steps that precede homolytic substitution, including C-C bond formation, are reversible under the reaction conditions.