Thermal decomposition of strained spiro(1-pyrazoline-3,1'-cyclopropanes)

Article abstract of DOI:10.1007/BF00696714

Pyrolysis (320-370 deg C) of polycyclic 1-pyrazolines 1 and 2, obtained by 1,3-dipolar cycloaddition of diazocyclopropane to 3,3-dimethylcyclopropene and spiro<2,3>hex-1-ene, yields complex mixtures of isomeric hydrocarbons, substituted methylenecyclopropanes being the main components.Pyrolysis of 6-ethenyl- (4) and 6-methoxy-6-methylcarbonyl-4,5-diazaspiro<2,4>hept-4-enes (6) at 310-320 deg C proceeds unambiguously to give vinyl- (18) and 1-methoxy-1-methylcarbonylspiropentanes (20) in ca. 85 and 95 percent yields with respect to the transformed pyrazolines.Dediazotization of pyrazoline 3 obtained from diazocyclopropane and benzvalene requires more drastic conditions (-440 deg C) and produces indane. - Keywords: spiro(1-pyrazoline-3,1'-cyclopropanes; methylenecyclopropanes and spiropentanes; pyrolysis; isomerization; NMR spectra.