1,3-Dipolar cycloaddition ofin situ generated 2,2-dimethyl-and 2,2-dichlorodiazocyclopropanes to 3,3-dimethylcyclopropene

2,2-Dimethyl- and 2,2-dichlorocyclopropyl-N-nitrosoureas were synthesized for the first time. Under the action of MeONa/MeOH at ?10°C, these compounds generate the corresponding 2,2-dimethyl- and 2,2-dichlorodiazocyclopropanes, which are readily trapped by 3,3-dimethylcyclopropene to give the products of 1,3-dipolar cycloaddition,viz., isomeric substituted spiro(2,3-diazabicyclo3. 1 .0] hex-2-ene-4,1 ′-cyclopropanes), in yields of about 70%,