Regioselectivity and kinetics of cobalt(II) chloride catalyzed phenylselenocyclization of 6-methyl-hept-5-en-2-ol

Abstract

Selenocyclization reactions are probably the most useful utilization of the electrophilic selenium(II) reagents. Addition of the reagents to the double bond triggers the nucleophilic attack of the suitably positioned pendant group resulting in the generation of a cyclic product. Due to the great diversity and versatility of pendant nuclephiles that can be used, these reactions have found widespread usage in some natural product synthesis, where the selenocyclization reaction represents the key step in their synthesis.1 Although, these reactions have established synthetic utility, very little has been done in improvement of understanding the mechanism and kinetics of these reactions. In this work we tried to achieve better insight in the mechanism of phenylselenoetherification of 6-methyl-hept-5- en-2-ol through the synthetic and kinetic study of the Co(II) chloride catalyzed cyclization under pseudo-first order conditions by UV–Vis spectrophotometry. Compared to the Lewis base catalyzed reactions, of this alkenol, much better regioselectivity was expressed with CoCl2. The obtained values for the rate constants have confirmed catalytic role of the CoCl2.