Ligand-Controlled Regiodivergent Ring Expansion of Benzosilacyclobutenes with Alkynes <i>en</i> Route to Axially Chiral Silacyclohexenyl Arenes
Xiaoxiao Tang, Yulang Tang, Ju Peng, Huimin Du, Liying Huang, Jiahui Gao, Shiyang Liu, Dongxu Wang, Wanshu Wang, Lu Gao, Yu Lan, Zhenlei Song
Abstract
A ligand-controlled regiodivergent and enantioselective ring expansion of benzosilacyclobutenes with internal naphthyl alkynes has been achieved by adjusting the ligand cavity size. The ligand ( S )-8 H -binaphthyl phosphoramidite, featuring small methyl groups on its arms, provides a spacious cavity that favors sterically demanding Si–Csp 3 ring expansion, predominantly yielding axially chiral ( S )-1-silacyclohexenyl arenes. In contrast, the ligand ( R )-spiro phosphoramidite, with bulky t -Bu groups on its arms, offers a compact cavity that facilitates less sterically demanding Si–Csp 2 ring expansion, leading primarily to axially chiral ( S )-2-silacyclohexenyl arenes. Density functional theory calculations delineate distinct mechanistic pathways for each ring expansion route and elucidate their regio- and enantioselectivity.