Nucleophilicities of Cyclic alpha-Diazo Carbonyl Compounds

The one-bond nucleophilic reactivities of seven cyclic alpha-diazo carbonyl compounds in dichloromethane were determined by analyzing the kinetics of their reactions with benzhydrylium ions (one-bond reference electrophiles) at 20 degrees C according to the Mayr-Patz equation. Though not calibrated for pericyclic reactions, the identified nucleophilicities also reflect relative reactivities of the alpha-diazo carbonyl compounds in 1,3-dipolar cycloadditions with dimethyl acetylenedicarboxylate. These (3+2)-cycloadditions primarily gave spirocyclic 3H-pyrazoles, which underwent thermal [1,5]-sigmatropic (van Alphen-Huttel) rearrangements to furnish 1H-pyrazole-fused tricyclic products.