Kinetic investigation of cyclization reactions of some terpenic alcohols

Abstract

Substituted tetrahydrofuran and tetrahydropyran ring systems are common structural units found in many bioactive natural products. Intramolecular heterocyclization of Δ4- and Δ5- alkenols is one of the fastest and easiest ways for obtaining cyclic ethers with very high structural diversity and possibility for further functionalization. In this work we investigated the influence of some Lewis bases (triethylamine, pyridine, quinoline, 2, 2’-bipyridne and piperidine) on rate constants of the electrophile-mediated cyclization of α- terpineol, linalool and nerolidol with PhSeCl and PhSeBr as a reagents. Reactions were performed under the pseudo-first order conditions, in the presence and absence of bases, by UV-VIS spectrophotometry in THF as a solvent. The obtained values for rate constants have shown that the reactions with phenylselenenyl bromide are slower then with chloride. Depending on the catalyst basicity and bulkiness, reaction rate is increased with a different degree compared to no catalyzed reaction. Steric hindrance in the rate determining ring closing phase is the one of the main reasons that influence the value of rate constants in these reactions.