Oxetane has been long known as a cyclic ether possessing ring-opening polymerizability, 1 and the cationic polymerization has been developed as a broadly applicable method for synthesizing functionalized polyethers. 2, 3 An interesting exception to this generally accepted concept was found by Corey et al. in ortho ester (5) synthesis by the Lewis acid catalyzed isomerization of oxetane esters (4)(eq 3 in Scheme 1). 4 Thereafter, we have ...