Oxidation of homochiral ketals by rhenium(VII) oxide. V

Oxidative α-acyloxylation of acetals with cyclic diacyl peroxides

Selective functionalization of the non-activated acetal α-position with formal retaining of the acetal fragment was realized using cyclic diacyl peroxides.

Dehydrative Re2O7-Catalyzed Approach to Dihydropyran Synthesis

Monoallylic 1,3- and 1,5-diols undergo Re₂O₇-mediated ionization to form allylic cations that engage in cyclization reactions to form dihydropyran products. The reactions give the 2,6-trans-stereoisomer as the major products as a result of minimizing steric interactions in a boat-like transition state. The results of these studies are consistent with cationic intermediates, with an intriguing observation of stereochemical retention in one example.

Direct proline-catalyzed asymmetric alpha-aminoxylation of aldehydes and ketones

The direct proline-catalyzed asymmetric alpha-aminoxylation of aldehydes and ketones has been developed using nitrosobenzene as an oxygen source, affording alpha-anilinoxy-aldehydes and -ketones with excellent enantioselectivity. Reaction conditions have been optimized, and low temperature (-20 degrees C) was found to be a key for the successful alpha-aminoxylation of aldehydes, while slow addition of nitrosobenzene is essential for that of ketones. The scope of the reaction is presented.