View Article Online/Journal Homepage/Table of Contents for this issue intermediate 12. Intermediate 12 may tautomerize to 13 which, on '5-exo'ring closure, should give compound 11. Substrates 5a, b, c underwent [3, 3] sigmatropic rearrangement at the vinyl propargyl sulfide segment instead of the aryl propargyl ether moiety. A lesser energy requirement for the sigmatropic rearrangement in vinyl propargyl systems10 compared to that in aryl ...