Ir‐Catalyzed Sulfur‐Directed Vinylic C─H Activation for the Stereoselective Synthesis of 1,3‐Dienes Using Alkynoates

Ir-catalyzed sulfur-directed C─H alkenylation of alkynoates proceeded by using aryl methallyl sulfides. When DMAD was employed, 1,3-dienes were initially formed and subsequently underwent thermal 1,5-sigmatropic rearrangement to yield secondary products with high stereoselectivitiy. Conversely, when aryl propiolates were used, the initially formed 1,3-dienes were obtained with high regio- and stereoselectivity in high brsm yield.

Abstract

Vinylic sp² C─H alkenylation with alkynoates was investigated in the presence of a cationic iridium catalyst using aryl 2-substituted allyl sulfides as substrates. In the reaction of dimethyl acetylenedicarboxylate, the double bonds were isomerized from the expected C─H alkenylated products, and sulfur-containing 1,3-dienes were obtained stereoselectively. A mechanism study suggested that the stereospecific isomerization involves thermal 1,5-sigmatropic rearrangement. On the other hand, in the case of phenylpropiolates, a regio- and stereoselective C─H alkenylation proceeded without isomerization when the reaction was stopped at low conversion.

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