Mechanism and Regioselectivity of the Cycloaddition of Thiones Derived from Meldrum’s Acid, Malonates, or Other Dicarbonyls

Several α,α-dioxothiones were generated in situ and reacted with 1,3-dienes of varying electronic and steric properties. It was found that thiones 10a and 11a reacted well with electron-rich or electron-poor dienes and are complementary in their regioselectivities when steric effects are at play. The calculated preferred mechanistic pathway implies a thiiranium zwitterion intermediate.

本研究原位生成了数种α,α-二氧代硫酮（α,α-dioxothiones），并使其与一系列电子性质与空间位阻特征各异的1,3-二烯烃（1,3-dienes）发生反应。实验结果表明，硫酮10a与11a可分别与富电子或缺电子二烯烃高效反应，且当空间位阻效应参与调控时，二者的区域选择性呈现互补特性。经计算得到的优势反应机理路径表明，该反应的关键中间体为环硫鎓两性离子（thiiranium zwitterion）。