The dehydrative coupling reactions of anti-b-hydroxyallylsilanes 5 and aldehydes provide 2,6-cis-dihydropyrans 27 by pathways involving oxonium ions that cyclize via boat-like transition state 21, with the intervention of oxonia-Cope rearrangements (21 ® 29).
抗 b-羟基烯丙基
硅烷 5 和醛的脱
水偶联反应通过涉及氧鎓离子的途径提供 2,6-顺式二氢
吡喃 27,氧鎓离子通过船状过渡态 21 环化,并参与 oxonia-Cope 重排 (21 ® 29) .