Silver(i)-catalyzed stereoselective Meyer-Schuster-type rearrangement: synthesis of densely substituted α-iodo α,β-unsaturated thioesters

Herein, we report our approach for a Meyer-Schuster type rearrangement to access alpha-iodo alpha,beta-unsaturated thioesters from propargyl thioalkynes using a silver(i) catalyst and N-iodosuccinimide as an electrophilic iodine source. The reaction proceeds smoothly for a range of propargyl thioalkynes, thus delivering tri- and tetrasubstituted olefins in good yields and, for a number of examples, (Z)-selectivity. The silver catalyst presumably plays a dual role involving both the activation of the pi-system by the alkynophilic Ag(i) and the activation of the NIS, ultimately leading to a sulfur-stabilized vinyl cation/ketenethionium intermediate. This reactive intermediate is trapped intramolecularly to yield an oxetane, which then readily undergoes decomposition to deliver the final product.