Rac-2′,3a,6,6,6′,6′-Hexamethyl-3a,3b,6,7-tetra-hydrospiro-[benzo[2,3]cyclopropa[1,2-c]pyrazole-1,1′-cyclo-hepta[2,4]diene]

Abstract

This note describes a novel reaction cascade in which a tosylhydrazone derivative of eucarvone undergoes a non-classical dimerization process under basic conditions. The key step in this sequence is a dipolar cycloaddition between a diazo species and a transient cyclopropene. A proposed mechanism for this sequence is presented that is supported by single crystal X-ray analysis of the resulting dimer. We believe this unique transformation is of note as it highlights a neat and efficient entry to complex polycyclic architectures containing an embedded pyrazoline moiety.

Keywords

• eucarvone
• dimerization
• cycloaddition
• tosylhydrazone
• 1,3-dipole
• molecular rearrangement
• Bamford-Stevens reaction