Unusual rearrangement of spiro β-lactams to 1,4-diazabicyclo[4,4,0]decanes and 1,4-diazabicyclo[4,3,0]nonanes. Synthesis of conformationally restricted σ-receptor ligands

Synthesis of 1,4-diazabicyclo4,4,0]decanes and 1,4-diazabicyclo4,3,0]nonanes was achieved by using 4-formyl spiro β-lactams as easily available starting materials. Furthermore, the application of this protocol to the preparation of conformationally restricted σ-receptor ligands was also performed. Theoretical calculations were carried out on a model reaction, in order to give some understanding of the reaction mechanism.