Kinetic studie of phenylselenoetherification of 2,6-dimethyl-hept-5-en-2-ol in the presence of some catalysts

Abstract

Tetrahydropyran- and tetrahydrofuran types of ethers are structural fragments of many natural products that can exibit significant biological activity. One of the most effective methods for their synthesis is cyclofunctionalization of unsaturated alcohols with phenylselenylhalides as reagents. Use of certain catalysts in these reactions increases yields and influences very high regio- and stereoselectivity. So far, small accomplishment has been achieved in the area of kinetics and mechanism of these reactions. In this work we presented results of kinetic investigation for phenylselenoetherification of 2,6-dimethyl-hept-5-en-2-ol with PhSeX (X= Cl, Br) in the presence of some Lewis bases as catalysts. All reactions were observed as reactions of pseudo-first order, where the reaction flow was monitored by measuring absorbance changes at the appropriate wavelength as a function of time. The reaction mixture was thermostated at 15 °C, and THF was used as solvent. Lewis bases: Et3N, pyridine and piperidine were used as catalysts. Obtained values for kobsd indicate that use of catalyst increases reaction rate. The reactions with PhSeCl as catalysts are faster then analogue reactions with PhSeBr. In addition, reaction rate depends on catalyst’s basicity, therefore the fastest reaction is the one with the strongest base- piperidine.