Syntheses of 2-and 3-Substituted Morpholine Congeners via Ring Opening of 2-Tosyl-1,2-Oxazetidine

Diastereoselective and diastereoconvergent syntheses of 2-and 3-substituted morpholine congeners are reported. Starting from tosyl-oxazatedine 1 and alpha-formyl carboxylates 2, base catalysis is utilized to yield morpholine hemiaminals. Their further synthetic elaborations allowed the concise constructions of conformationally rigid morpholines. The observed diastereoselectivities and the unusual diastereoconvergence in the photoredox radical processes seem to be the direct consequence of the avoidance of pseudo A1,3 strain between the C-3 substituent and the N-tosyl group and the anomeric effect of oxygen atoms.