Specific Formation of Cyclic Tetramer in Oligomerization of (R)-tert-Butyloxirane with Boron Trifluoride Etherate, and NMR and ORD Studies of the Cyclic Tetramer

Abstract

The reaction of (R)-tert-butyloxirane with boron trifluoride etherate as catalyst results in the specific formation of a cyclic tetramer, (2R,5R,8R,11R)-2,5,8,11-tetra-tert-butyl-1,4,7,10-tetraoxacyclododecane, in high yield. The specificity of the reaction can be ascribed to steric requirements caused by the bulky tert-butyl group. Every monomeric unit, –(O—CH(tert-C₄H₉)—CH₂—), in the cyclic tetramer preferably takes a G⁺G⁺T conformation, in contrast to the G⁺G⁻T conformation in the corresponding linear polymer. The ORD spectra of the cyclic tetramer are nearly the same in cyclohexane, in benzene, and in chloroform. The lack of solvent effect upon the ORD spectra may be explained in terms of the structure of the cyclic tetramer, in which the ether oxygen atoms wholly surrounded by the hydrocarbon parts of the cyclic tetramer are barely accessible to the solvent molecules.