Interception of Alkynyl Tetracoordinate Borons with Sulfur Electrophiles beyond the Zweifel Pathway

Abstract

Zweifel reaction is a powerful strategy to construct olefins from alkenyl tetracoordinate borons in organoboron chemistry, however, it usually only involves one functional group migration and then undergoes an elimination process affording alkenes or alkynes exclusively. Herein, we disclose several intriguing interception of alkynyl tetracoordinate borons with sulfur electrophiles. Wherein, the substituted benzothiophenes are accessed by consecutive 1,2‐migrations and intramolecular electrophilic substitution, meanwhile, the challenging and elusive five/four‐membered boracycles are easily assembled, and an approach to alkenyl sulfides with good stereoselectivity was developed as well. Moreover, by adding readily available deuterium sources, the tetrasubstituted deuterated alkenyl sulfides with high deuteration rates are constructed. These protocols not only improve atom economy by prohibiting the elimination of Zweifel intermediate, but also enriches the reaction modes of alkynyl tetracoordinate borons achieving versatile value‐added sulfur‐containing molecules. Mechanistic investigations illustrate that dichlorosulfoxide (SOCl2) and dialkylaminosulfur trifluoride‐type reagents (DAST‐type) as surfur sources could promote dual 1,2‐aryl migration of alkynyl tetracoordinate borons, which are distinct from traditional Zweifel reaction, and the regulation of steric hindrance could also make four‐membered boracycles and alkenyl sulfides feasible. And these transformations feature novel reaction modes and unusual reaction mechanisms with valuable products in high efficiency.