Waddell Michelle K, Bekele Tefsit, Lipton Mark A
Department of Chemistry and Cancer Center, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907-2084, USA.
J Org Chem. 2006 Oct 27;71(22):8372-7. doi: 10.1021/jo061088n.
A series of acetoxy-substituted enyne-allenes, fused to cyclopentene and cyclohexene ring systems, were synthesized and treated with methyllithium to generate the corresponding enolates. It was found that whereas the cyclohexannulated examples underwent either C2-C7 (Myers-Saito) cycloaromatization or C2-C6 (Schmittel) cyclization depending on their terminal subsituents, the cyclopentannulated examples either failed to cyclize altogether or underwent C2-C7 cyclization. Both of these results lie in contrast to the behavior of their benzannulated analogues, which underwent exclusive C2-C6 cyclization independent of substituents. These findings are rationalized on the basis of both ring strain effects and the steric encumbrance of the terminal alkynyl and allenyl subsituents.
一系列与环戊烯和环己烯环体系稠合的乙酰氧基取代的烯炔-丙二烯被合成出来，并与甲基锂反应生成相应的烯醇盐。结果发现，对于环己烷稠合的例子，根据其末端取代基的不同，会发生C2-C7（迈尔斯-斋藤）环化芳构化或C2-C6（施密特尔）环化反应；而环戊烷稠合的例子要么完全无法环化，要么发生C2-C7环化反应。这两个结果与它们的苯稠合类似物的行为形成对比，苯稠合类似物无论取代基如何都只发生C2-C6环化反应。这些发现基于环张力效应以及末端炔基和丙二烯基取代基的空间位阻得到了合理的解释。
