Conversion of 2-Sulfinylated 2-Alkenoate Esters to (2E,4E)-2,4-Alkadienoate Esters by Pyrolysis

Thermal reaction of ethyl (2E)-2-phenylsulfinyl-2-alkenoates (E-2) prepared from aldehydes and ethyl 2-phenylsulfinylacetate have been investigated. Refluxing of E-2 or their Z-isomers in xylene resulted in the formation of ethyl (2E,4E)-2,4-alkadienoates accompanied by ethyl (2E)-4-hydroxy-2-alkenoates. Ethyl 2-cycloalkylidene-2-phenylsulfinylacetates were found to be more susceptible to pyrolysis. The enoate esters (2) undergo migration of their carbon-carbon double bond and then [2,3]sigmatropic rearrangement to benzene-sulfenate esters, followed by thermolytic extrusion of a benzenesulfenic acid probably via ethyl (2E)-4-phenyl-sulfinyl-2-alkenoates to afford ethyl (2E,4E)-2,4-alkadienoates.