Intramolecular rearrangement of epoxides generated in situ over titanium silicate molecular sieves

Open chain unsaturated alcohols I, having the general formula R1R2C=CH(CH2) (n)CR1R2OH (where R-1, R-2 = H or CH3, and n = 13) and carbocyclic unsatura ted alcohols of similar type have been efficiently cyclized to the correspo nding hydroxytetrahydrofuran or hydroxytetrahydropyran over titanium silica te molecular sieves (TS-1 and Ti-beta), in one pot under mild liquid phase reaction conditions using dilute hydrogen peroxide as oxidant. When the hyd roxy nucleophile may attack either of the activated carbon atoms of the epo xides generated in situ, to lead to a derivative of tetrahydrofuran or tetr ahydropyran, the former exclusively formed. The regioselectively for such r eaction is 100%. When R-1 or R-2 = CH3, among the diasteroisomeric products trans predominates over cis. In this cyclization reaction titanium silicat e epoxidizes the olefin and successively catalyzes the opening of the oxira ne ring via intramolecular attack of hydroxy oxygen. Thus the behavior of t itanium sites is bifunctional in nature. However, for bicyclic unsaturated alcohols, because of geometric restriction, activity of medium pore TS-1 is very low. Ti-beta synthesized by dry gel conversion has been found to be a n efficient catalyst in oxidative cyclization of such bulky organic substra tes as cu-terpineol, isopulegol, and trans-p-menth-6-ene-2,8-diol to their corresponding tetrahydrofuranols or tetrahydropyranols with a very high reg ioselectivity. (C) 1999 Academic Press.