THE STEREOCHEMISTRY OF POLYENE CYCLIZATION
THE STEREOCHEMISTRY OF POLYENE CYCLIZATION
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DOI：
10.1021/ja01624a038
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发表时间：
1955-01-01
影响因子：
15
通讯作者：
BURGSTAHLER, AW
中科院分区：
文献类型：
--
作者：
STORK, G;BURGSTAHLER, AW
机械上重要的是，虽然六元环是 1, 5-二烯环化的常见产物，但五元环也在 2, 7-二甲基-2, 6-辛二烯 (I) 3 环化中获得 (a) 和 (b) 在涉及芳环攻击的环化中获得，这导致形成不同数量的螺环，如 II (R=H) 一样。 4 在 I 的情况下，这些结果很容易合理化，它只涉及有利于五元环形成的空间和电学因素的组合，而在 II 的情况下，芳香系统的低亲核性允许反应与更好的引发碳鎓离子的形成不一致地进行。在其他条件不变的情况下，当式II中的R是甲基时，螺环形成的抑制充分说明了在该反应中优先形成六元环。 6
It is mechanistically significant that although sixmembered rings are the usual products from the cyclization of 1, 5-dienes, five-memberedrings also have obtained (a) in the cyclization of 2, 7-dimethyl-2, 6-octadiene (I) 3 and (b) in cyclizations involving attack of an aromatic ring which lead to theformation of variable quantities of spirans as with II (R=H). 4 These results are rationalized easily in the case of I which simply involves a combination of steric and electrical factors favorable to five-membered ring formation and in the case of II the low nucleophilicity of the aromatic system allows the reaction to proceed non-concertedly with the formation of the better initiating carbonium ion. The preference for the formation of six-membered rings in this reaction, ceteris paribus, is well illus-trated by the suppression of spiran formation when R in formulaII is a methyl group. 6