Ring-selective syntheses of homochiral oxepanes and tetrahydropyrans from carbohydrates via intramolecular nitrone or nitrile oxide cycloadditions
Abstract
Intramolecular 1,3-dipolar cycloadditions of nitrones formed from 3-O-allyl-1,2-O-isopropylidene-α-D-pentodialdofuranoses afford oxepanes or tetrahydropyrans selectively whereas the intramolecular cycloadditions of nitrile oxides derived from the same aldehydes give exclusively tetrahydropyrans.