Dienes addition reactions with selenium electrophiles

The lactonization of 5,7-dienoic acids with selenium and sulfur electrophiles generates 8-lactones by regioselective 1,4-addition to the diene (equation 36).s2a With substitution at the 8-position, reaction with PhSeCl or PhSCl gave a 1 1 mixture of rapidly interconverting 1,2- and 1,4-addition products. This inter-conversion, presumably via a 1,3-rearrangement,S2b was not observed with the alkylthio adduct. An example of conjugate cyclization of an enyne system to form an allenyl product has also been reported (equation 37).112... 

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