ChemInform Abstract: Stereoselective trans- and cis-Dihydroxylations of 2H-Pyranyl and Dihydropyridinyl Heterocycles Synthesized from Formal [3 + 3]-Cycloaddition Reactions of α,β-Unsaturated Iminium Ions with 1,3-Dicarbonyl Equivalents

We describe here an inherent problem in direct epoxidation of the endocyclic olefin in 2H-pyrans fused to 2-pyrones. Such difficulties led to the development of highly stereoselective trans- and cis-dihydroxylations of these olefinic systems in both 2H-pyrans and dihydropyridines fused to a 2-pyrones or a 2-cyclohexenone. Protocols for the removal of the activated allylic hydroxyl group are also reported.