Intramolecular Ene Reaction of Epoxyallylsilanes: Synthesis of Allyl- and Vinylsilane-Functionalized Cyclohexanols

Epoxyallylsilanes bearing the bulky tert-butyldiphenylsilyl group undergo an uncommon tandem rearrangement−cyclization process upon treatment with Lewis acids. Two pathways for the carbonyl ene reaction are observed: one leading to allylsilane−cyclohexanols when the epoxyallylsilane (28−31) is nonsubstituted, 2-, or 4-monosubstituted and other leading to vinylsilane−cyclohexanols when the epoxyallylsilane (24−27) is 2,4-disubstituted or trisubstituted. An explanation for the observed regio- and stereoselectivity is advanced and a reliable mechanism proposed.带有大位阻叔丁基二苯基硅基（tert-butyldiphenylsilyl）的环氧烯丙基硅烷（epoxyallylsilanes）经路易斯酸（Lewis acids）处理后，可发生罕见的串联重排-环化过程。研究发现其存在两条羰基烯反应（carbonyl ene reaction）路径：当环氧烯丙基硅烷（28~31）未取代、2位或4位单取代时，产物为烯丙基硅烷-环己醇类化合物；当环氧烯丙基硅烷（24~27）为2,4-双取代或三取代时，产物则为乙烯基硅烷-环己醇类化合物。文中针对所观测到的区域选择性与立体选择性给出了解释，并提出了可靠的反应机理。