Photochemical [2 + 2] cycloaddition reactions of 6-alkenyl-3-phenylcyclohex-2-en-1-ones: using biradical conformation control to account for exceptions to the “rule of five”
作者:Stephen A. Bradley、Brian J. Bresnan、Sylvia M. Draper、Niall W. A. Geraghty、Mark Jeffares、Thomas McCabe、T. Brian H. McMurry、John E. O'Brien
DOI:10.1039/c0ob01131b
日期:——
A series of 6-alkenyl-3-phenylcyclohex-2-enones has been synthesised and the structures of the products obtained from them on irradiation have been determined. The 6-propenyl compounds afforded a tricyclic âparallelâ [2 + 2] cycloaddition product and a bicyclic enone resulting from hydrogen abstraction in the biradical intermediate. The 6-butenyl and 6-pentenyl analogues gave âcrossedâ cycloaddition products only. Although the regiochemistry of these cycloaddition reactions cannot be explained in terms of the ârule of fiveâ, it is compatible with the concept of âbiradical conformation controlâ which is based on a consideration of the energy and structure of the possible 1,4-biradical intermediates.
合成了一系列6-烯基-3-苯基环己-2-烯酮,并确定了由它们辐照得到的产物的结构。 6-丙烯基化合物提供了三环-平行-[2 + 2]环加成产物和双自由基中间体中夺氢产生的双环烯酮。 6-丁烯基和6-戊烯基类似物仅产生“交叉”环加成产物。虽然这些环加成反应的区域化学不能用“五规则”来解释,但它与基于对能量和结构的考虑的“双自由基构象控制”的概念是兼容的。可能的1,4-双自由基中间体。