S-adenosyl-L-methionine (SAM), a sulfonium-based cofactor, plays an important role in numerous biological processes as methyl donor. Inspired by the function of sulfonium motif in this nature's synthetic toolkit, we here present an aryne-activation strategy that the sulfonium intermediates in situ generated from thioethers display unique reactivity toward alkyl group transposition. Experimental and theoretical studies indicate that the reaction occurs in an intermolecular fashion where the TfO--incorporated [K(18-crown-6)] complex acts as a key promoter for this thermodynamically favored process. Next, a series of robust, easy-to-prepare sulfonium salts are designed and developed as electrophilic alkylation reagents accordingly. Both systems feature for broad scope, excellent selectivity, and simple operation. Moreover, we highlight the synthetic value through molecular editing and late-stage modification of complex scaffolds or even active pharmaceutical ingredients.