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Cyclopropylazoarenes containing methoxy groups in the aromatic ring give the corresponding N-arylpyrazolines on the reflux in o-dichlorobenzene or on SnCl2 catalysis at 80 °C in good yields. The products can be smoothly oxidized into the corresponding pyrazoles. Thermolysis of cyclopropylazoarenes containing hydroxy groups in the aromatic ring proceeds more complicated. Thus in the case of resorcin azo derivative, strong resinification of the reaction mixture is observed and the corresponding N-arylpyrazoline is isolated only in −40% yield. Under similar conditions, thermolysis of 1-cyclopropyl- and 1-(1-methylcyclopropyl)azo-2-naphthol proceeds otherwise and unexpectedly leads to naphtho[1,2-d]oxazole derivatives with degradation of the cyclopropane ring.

1-Pyrazolines, obtained by 1,3-dipolar cycloaddition of diazocyclopropane to N-phenyl- and N-cyclohexylmaleimides, undergo complete dediazoniation at 175 °C for 10–16 h with the formation of spiro[3-azabicyclo[3.1.0]hexane-6,1′-cyclopropane]-2,4-diones 3 (80–89%) and isomeric 3-cyclopropyl-1H-pyrrole-2,5-diones 4. On the example of 3-cyclopropyl-1-phenyl-1H-pyrrole-2,5-dione, it was shown that compounds 4 are able again to enter into 1,3-dipolar cycloaddition with diazomethane or diazocyclopropane with the reaction in the case of diazocyclopropane being nonselective and leading to two regioisomeric pyrazolines in the ratio ∼1.7: 1, thermolysis of which, conversely, proceeds with high selectivity and exclusively affords a spiropentane derivative. An action of the aqueous methanol solution of sodium hydroxide on the spiropentanes fused with succinimide fragment and subsequent acidification of the salts obtained lead to stable cis-amidoacids of spiropentane series.

Methyl 2-cyclopropyl-2-diazoacetate was synthesized from acetylcyclopropane in few chemical steps in ∼55% total yield. Its copper or rhodium-catalyzed dediazoniation exclusively proceeds through the intramolecular isomerization of generated cyclopropyl(methoxycarbonyl)carbene to 1-methoxycarbonylcyclobutene, irrespective of the presence or the absence of unsaturated compounds. However, in the presence of acrylates or strained cycloalkenes, this diazo ester is being slowly involved into the 1,3-dipolar cycloaddition, giving cyclopropyl-substituted pyrazolinecarboxylates, which in case of 1-pyrazolines easily lose nitrogen molecule to selectively afford 1-cyclopropylcyclopropanecarboxylate derivatives.

Cyclopropyldiazonium generated by basic decomposition of N-cyclopropyl-N-nitrosourea easily entered into an azo coupling reaction with 5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one (2) to give the corresponding cyclopropylhydrazone in up to 90% yield. Competitive processes occurring under the conditions of cyclopropyldiazonium generation by nitrosation of cyclopropylamine with butyl nitrite mainly include nitrosation of the starting pyrazolone 2. Subsequent transformations of the resulting heterocyclic 3-methyl-1-phenyl-1H-pyrazole-4,5-dione 4-oxime yield 4-[cyclopropyl(oxido)imino]-5-methyl-2-phenyl-2,4-dihydro-3H-pyrazol-3-one.

Raney nickel-catalyzed hydrogenation of 5-substituted spiro[cyclopropane-3-(1-pyrazoline)]-5-carboxylates occurs with N—N bond cleavage with simultaneous cyclocondensation to give 3-aminopyrrolidin-2-ones containing a spirocyclopropane fragment. The presence of the second ester group in the pyrazoline side chain, in the position ensuring the formation of a five-membered ring results in 6,11-diazadispiro[2.1.4.2]undecane-7,10-dione, the product of double cyclocondensation of the intermediate diamine. Hydrogenation of the aryl-substituted spiro[cyclopropane-3-(1-pyrazolines)] in the presence of acetone affords hexahydrospiro[cyclopropane-4-pyrimidines], which can be converted into the cyclopropane-containing 1,3-diamines in the individual state or as salts.

Prolonged storage (45–60 days) of N-methyl- or N-cyclopropylaziridine-2-carboxylates leads to their dimerization through the N—C(3) bond cleavage to form 1,3-disubstituted 2-methylimidazolidine-2,4-dicarboxylates in high yields. Prolonged storage of 1-benzyl-aziridine-2-carboxylate (like the reactions of alkyl pyruvates with primary amines) results in cyclocondensation to yield 3-pyrrolin-2-one derivative.

3-Cyano- and 3-(alkoxycarbonyl)spiro[2-pyrazoline-5,1’-cyclopropane] and 5-phenylspiro[1-pyrazoline-3,1’-cyclopropane] undergo unusual transformations into 3(5)-substituted 5(3)-(2-hydroperoxyethyl)pyrazoles in the presence of atmospheric oxygen. The conditions for the formation of hydroperoxides (e.g., in oxygen-saturated solutions of spiro[2-pyrazoline-5,1’-cyclopropanes] in CHCl3) and their conversion into (2-hydroxyethyl)pyrazoles or the corresponding nitrates under the action of nitrosating reagents were considered.

Reactions of 2-fluoro-3-methylbuta-1,3-diene with diazomethane in ether at 15 °C and with diazocyclopropane generated in situ by decomposition of N-cyclopropyl-N-nitrosourea in the presence of K2CO3 in CH2Cl2 at –10 °C selectively involve the double bond at the methyl group to give 3-(1-fluorovinyl)-3-methylpyrazolines. Thermal dediazotization of the latter at 250 °C yields 1-(1-fluorovinyl)-1-methylcyclopropane and -spiropentane 5, which are capable of isomerizing, under more severe conditions (400—600 °C), into 1-fluoro-2-methylcyclopent-1-ene and 5-fluoro-4-methylspiro[2.4]hept-4-ene (7), respectively. Spiropentane derivative 5 partially isomerizes into 1-fluoro-2-methyl-3-methylidenecyclohex-1-ene. In a similar way, thermolysis of 6-(2,3,3-trifluorocyclobut-1-enyl)-4,5-diazaspiro[2.4]hept-4-ene at 400 °C gives a mixture of 1-(spiropentyl)-2,3,3-trifluorocyclobut-1-ene and 2,3,3-trifluoro-1-(2-methylidenecyclobutyl)cyclobut-1-ene. Thermolysis of 1-cyclopropyl-2,3,3-trifluorocyclobut-1-ene at 550—620 °C affords a mixture of 1-(trifluorovinyl)cyclopentene and 2,3-difluorotoluene.

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.

Decomposition of N-cyclopropyl-N-nitrosourea under the action of K2CO3 or KOH containing 15—20% of H2O at 0—7 °C gives rise to cyclopropyldiazonium, which reacts with some β-diketones, methyl cyanoacetate, or malonodinitrile to form the corresponding cyclopropylhydrazones. The latter compounds are analogous to products of azo coupling and isomerization of aryldiazonium ions with the above-mentioned substrates. These transformations provide the first example of azo coupling of the cyclopropyldiazonium ion in the series of activated aliphatic CH acids.

N-(2-Methylenecyclopropyl)-N-nitrosourea (2) was synthesized for the first time (yield 70%) and its decomposition induced by bases was studied. In particular, treatment with MeONa/MeOH at-30°C in the presence of methyl methacrylate gives the corresponding I-pyrazoline stereoisomers, the products of [3+2]-cycloaddition of diazo-2-methylene-cyclopropane (1) generatedin situ. Decomposition of2 on treatment with K2CO3 at 0–5°C in the presence of acrylonitrile also proceeds as [3+2]-cycloaddition: however, the expected 2-pyrazoline easily isomerizes into 5(3)-isopropenyl-3(5)-cyanopyrazole. Buta1,2,3-triene is the main product of base-induced decomosition of2 in the absence of unsaturated substrates.

Strained polycyclic spiro(1-pyrazoline-3,1′-cyclopropanes) react with acetyl or benzoyl chlorides at 0–15 °C regioselectively to give in high yields corresponding 1-acyl-3-(2-chloro-ethyl)-2-pyrazolines. Under the same conditions 6-ethenyl-4,5-diazaspiro[2,4]hept-4-ene gives a mixture of two pyrazolines resulting from the acyl group attack directed at different nitrogen atoms. Bicyclic pyrazolines-2 obtained by acylation of the cycloaddition products of diazocyclopropane with 3,3-disubstituted cyclopropenes transform under the action of hydrogen chloride to 1,4,5,6-tetrahydropyridazines in high yields.