Synthesis of Functionalized Thietanes via Electrophilic Carbenoid-Induced Ring Expansion of Thiiranes with Sulfonium Acylmethylides as Carbene Precursors.

Various functionalized thietanes were prepared from thiiranes via an electrophilic ring expansion with rhodium carbenoids as electrophiles generated from safe and readily accessible dimethylsulfonium acylmethylides. The reaction appears to proceed through electrophilic metallocarbenoid-induced activation of thiiranes, nucleophilic ring-opening of the activated thiiranes with dimethyl sulfide as a transient nucleophile, and nucleophilically intramolecular cyclization. The Umpolung from the nucleophilic ylides to the electrophilic carbenoids plays an important role in both the activation and ring opening of thiiranes and subsequent cyclization. The current method provides a new strategy for the efficient preparation of functionalized thietanes from readily available thiiranes.