An unexpected ring formation in morphine chemistry

Reaction of (7R)-N-benzyl-N-nor-7-bromoneopinone dimethyl acetal (2) with primary or secondary amines (RNH2, R1R2NH) resulted in 9-amino-substituted hasubanan derivatives; in particular, modification of the 9-(2-hydroxyethyl)amino derivative in subsequent steps gave products 8 with a 9-(oxazolidin-2'-one-3'-yl) substituent. 1 H and 13 C NMR spectra did not provide definitive evidence for the supposed structure and reaction mechanism, but X-ray analyses of compounds 8a and 8d confirmed both structures.