[3,3]Sigmatropic ring expansion of cyclic thionocarbonates. Highly stereoselective synthesis of (Z)- or (E)-double bonds by controlling chairlike-boatlike transition states in the [3,3]sigmatropic rearrangement of 8-membered thionocarbonates

Article abstract of DOI:10.1016/S0040-4020(01)88312-5

A highly stereoselective synthesis of (Z)- or (E)-double bonds in 10-membered thiolcarbonates (3) was successfully conducted by controlling the chairlike-boatlike transition states in the [3,3]sigmatropic rearrangement of 8-membered thionocarbonates (2). The geometry of the product appeared to be highly dependent on the substituent pattern in the allylic system of the substrates (1). The 10-membered thiolcarbonates (3) were readily converted to (Z)- or (E)-allylic thiolcarbonates (11). Treatment of (Z)-3j or 3i with lithium in liquid ammonia afforded (Z)-trisubstituted or tetrasubstituted olefins (12j and 12i) in high yields.