Expeditious Synthesis of Enantioenriched Tetrahydropyrans via Chemoselective C−N bond Cleavage of Aza-Oxa-Bicyclo[3.2.1]Octanes

A rapid synthesis of enantioenriched 2,3,4-trisubstituted tetrahydropyrans in good yields and stereoselectivities is reported. The first step is a domino organocatalytic reaction between ambident electrophilic and 1,4-bis-nucleophilic 1,2-ketoamides and 1,3-bis-electrophilic enals, leading to aza-oxa-bicyclo[3.2.1]octane. Then, the TiCl4/Et3SiH system ensures a chemoselective cleavage of the C−N bond and affords the desired trisubstituted tetrahydropyran in good yield and with conservation of the precursors optical purity. This final synthetic operation includes two consecutive oxocarbenium ion formation and reductions. (Figure presented.). © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim