OXIDATION OF FULLY PROTECTED GLYCALS BY HYPERVALENT IODINE REAGENTS

摘要

A new application of organoiodine(III) is presented. Fully protected glycals are directly converted into 2,3-dihydro-4H-pyran-4-ones by [hydroxy(tosyloxy)iodo]benzene (PhI(OH)OTs, 1). The detailed study reveals that this conversion is independent of the relative stereochemistry as well as the nature of protection on the pyran ring. 3-O-Silyl groups are most smoothly converted into the keto group giving 2,3-dihydro-4H-pyran-4-ones in yields up to 74%. In contrast, 4,6-di-O-acetyl-3-deoxyglucal (19) affords the rearranged oxidation product 32. Both observations can be reconciled by the proposed mechanism. [References: 60]