Insertion into Donor-Acceptor Cyclopropanes with Carbon-Sulfur Moieties Derived from Sulfoxonium Ylides and Elemental Sulfur.

The (3 + 2) cycloaddition of donor-acceptor cyclopropanes (DACs) with carbon-sulfur 2π components has become an emerging method to rapidly assemble tetrahydrothiophenes. Starting materials donating the carbon-sulfur unit are often isolated from thionation of carbonyls or carboxylic acid derivatives. Herein we report a method for the cycloaddition of DACs with carbon-sulfur moieties presumably formed in situ via β-sulfuration of α-carbonyl sulfoxonium ylides with elemental sulfur. The insertion occurred without the assistance of Lewis acid, perhaps due to the strongly polarized carbon-sulfur-containing intermediate. The hitherto challenging α-monosubstituted tetrahydrothiophenes were obtained with a wide range of tolerated functionalities.