Generation and reactions of diazo-3,3-dideuterio-2-methylidenecyclopropane and isomerization of 3",3"-dideuterio-2"-methylidenespiro[4,5-dihydropyrazole-5,1"-cyclopropanes] into isopropenylpyrazoles

Abstract

N-(1,3,3-Trideuterio-2-methylidenecyclopropyl)-N-nitrosourea was synthesized and its decomposition on treatment with K₂CO₃ in the presence of acrylonitrile and ethyl acrylate or on treatment with MeONa in the absence of unsaturated substrates was studied. The rate of decomposition of the nitrosourea is much lower than that of the nondeuterated analog. The use of acrylates for trapping the intermediate 3,3-dideuterio-1-diazo-2-methylidenecyclopropane results in the corresponding 2"-methylidenespiro[4,5-dihydropyrazole-5,1"-cyclopropanes] containing two deuterium atoms in the cyclopropane fragment. The resulting dihydropyrazoles are isomerized almost entirely over a period of 1—3 days to give a mixture (∼1 : 1) of isopropenylpyrazoles in which both deuterium atoms occur either in the methyl or in the methylidene groups of the isopropenyl substituent. A possible mechanism of this transformation is considered.