Stereoselective synthesis of oxa-bowls by nucleophilic addition to oxonium ions: Observation of nucleophile-dependent hydride migration

A simple and reliable platform was developed for the synthesis of symmetrical oxa-bowls through the Lewis acid mediated etherification of dimethyl acetals. An intramolecular hydride transfer was observed with the use of electron-rich aryl nucleophiles, which also gave access to unsymmetrical oxa-bowls. A general strategy is developed for the stereoselective synthesis of symmetrical oxa-bowls through the Lewis acid mediated generation of oxonium ions from bis-acetals and their subsequent trapping with a variety of nucleophiles. Hydride migration is observed with the use of trimethoxybenzene as a nucleophile with rigid acetal precursors. This method is extended to the synthesis of unsymmetrically substituted oxa-bowls. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.