Regiodivergent Synthesis of 1- and 2-Arylsulfonyl 1,3-Dienes

In the course of a study of the alkoxyallylation of allenic sulfones through the use of π-allylpalladium chemistry, we discovered an isomerization of allenic sulfones to arylsulfonyl 1,3-dienes. Under conditions of palladium catalysis in the presence of acids such as acetic acid, allenic sulfones are converted to 1-arylsulfonyl 1,3-dienes. On the other hand, nucleophilic catalysis using triphenylphosphine in the presence of a proton shuttle yields 2-arylsulfonyl 1,3-dienes. Thus, either regioisomer of the arylsulfonyl diene can be prepared at will based on changes in reaction conditions.