3,3]Sigmatropic ring expansion of cyclic thionocarbonates. 8. 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

Abstract

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.