The Swern Oxidation: First example of direct oxidation of 2-pyrazolines with “activated” DMSO

1,3-Dipolar cycloaddition of 2-diazopropane to conjugated dienes 1 and α,β-unsaturated ketones 5 is taking place regiospecifically to give cycloadduit 4 and 6. The reaction of 2-pyrazolines derivatives with dimethylsulfoxide and oxalyl chloride under Swern conditions led to a pyrazolenines 7 and 8.