Diastereoselective
and diastereoconvergent syntheses of 2- and
3-substituted morpholine congeners are reported. Starting from tosyl-oxazatedine1and α-formyl carboxylates2, 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 A1,3strain
between the C-3 substituent and the N-tosyl group and the anomeric
effect of oxygen atoms.