Stereospecific [1,2]-rearrangement of a spirocyclic ammonium ylide with ring expansion sequence

Enantiomerically pure bicyclic 1,4-oxazepinone was obtained by the Cu(II)-catalyzed decomposition of an α-diazo carbonyl compound tethered to a chiral morpholinone, through the cascade evolution of the spirocyclic ammonium ylide formed. LiAlH₄ reduction and transesterification of the lactone moiety of the oxazepinone afforded pure chiral pyrrolidine and 3-prolinone bicyclic hemiacetal, respectively, both bearing a quaternary stereocentre.