The thermaldecomposition of spiro-1-pyrazolines 2 obtained by the cycloaddition of exocyclic α,β-unsaturated ketones with diazomethane gives spirocyclopropanes 4 with high selectivity and the new β-methyl-3-benzylidene derivatives 3. The configuration and conformation of the thermolysis products 3 and 4 were elucidated by different n.m.r. methods.
that this cycloaddition is regio- and stereoselective affording trans- and cis- spiro-1-pyrazolines. Spiro-1-pyrazolines were converted into spiro-2-pyrazolines on acid-catalysed isomerization. Conformation and relative configuration of compounds prepared has been elucidated by various one- and two-dimensional n.m.r. methods.