Kinetic investigation of phenylselenoetherification of some Δ4-alkenols in presence of catalytic amount of CoCl2

Abstract

The phenylselenoetherification of unsaturated alcohols is the one of the most rapid and convenient methods for formation of THF and THP type of rings. The convenient position of a double bond and a hydroxyl group in an alkenol can easily lead to formation of corresponding cyclization product. The reaction of selenium electrophiles with alkenols is a stereospecific anti addition where the nucleophile (pendant hydroxyl group) attacks usually at higher substituted carbon atom (Markownikoff stereoselectivity).1 Despite the established synthetic utility of these selenofunctionalization reactions, there is no many report on a detailed kinetic investigation of these transformations.2 In previous work it was found that in the presence and absence of various additives these reactions follow the mechanism of bimolecular nucleophile substitution SN 2 pathway.2c In this work we reported the kinetic study of the cyclization of some Δ4-alkenols with PhSeX (X=Cl, Br) in presence of catalytic amount of CoCl2. We investigated the influence of olefinic and carbinol substitution pattern in some Δ4 -alkenols on the rate constants of the cyclization under the pseudo-first order conditions, in the presence and absence of CoCl2, by UV-VIS spectrophotometry. Reactions were carried out in the THF as a solvent. The obtained values for rate constants have shown that the reactions with phenylselenenyl bromide are slower then with chloride. Reactions with CoCl2 present are faster then without one. Values for rate constants strongly depend on a substitution pattern of used alkenol.