Captodative substituent effects XXI. : Synthesis of selenenylated captodative olefins via selenenyl halide addition to olefins bearing electron-withdrawing substituents

Abstract

Addition of methane- and benzeneselenenyl bromide or chloride and benzene sulfenyl chloride to carbon-carbon double bonds substituted by electronwithdrawing groups is achieved in solvents of different polarity. Two regioisomeric adducts 6 and 7 or 8 and 9 are generally formed, which can be interconverted by equilibration in refluxing acetonitrile. It is of mechanistic interest that the regioisomers may also derive from selenenyltrihalide adducts. In comparison to acrylic esters, the propiolic ester reacts more slowly, producing mainly the α-selenenyl adduct. Dehydrohalogenation of adducts provides a general and valuable method for the preparation of olefins carrying methyl or phenylselenenyl groups in α-position to electron-withdrawing substituents.