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The main achievements and development trends of the past 10–15 years related to the catalytic cyclopropanation of unsaturated compounds with diazomethane are integrated and analyzed. The attention is focused on the most efficient catalysts based on palladium compounds. Data on the effects of substrate structure and nature of catalyst components on the regio- and stereoselectivity of these reactions are systematized. Characteristic features of safe methods for diazomethane generation are considered, including the use of membrane technologies and continuous-flow and in situ preparation methods, which have prospects for industrial application. The bibliography includes 281 references.

The Pd-catalyzed cyclopropanation of 3a,4,7,7a-tetrahydro-1H-indene with diazomethane unexpectedly affords monoand dicyclopropanation products in good yields, the cyclopentene double bond being approximately three times more reactive than the cyclohexene one. In contrast, similar independent competitive cyclopropanation of a cyclopentene–cyclohexene mixture has shown that cyclohexene exhibits an abnormally low reactivity differing by about two orders of magnitude.

A new process of “inverted” formal [3 + 2]-cycloaddition of donor–acceptor cyclopropanes (DACs) to allylic systems to give polyfunctionalized cyclopentanes has been developed. Unlike the classical version of formal [3 + 2]-cycloaddition, a DAC acts in this process as a two-carbon synthon (1,2-zwitterionic reactivity type), while an alkene acts as a three-carbon synthon. Tetramethylethylene, allylbenzenes, homoallylbenzene, terminal and internal aliphatic alkenes, and methylenecyclobutane were successfully used as alkenes. Furthermore, in order to suppress annulation at the aromatic ring in 2-arylcyclopropane-1,1-dicarboxylates and enhance the selectivity of the reaction with the allylic system of alkenes, we suggested a new approach for managing the reactivity of DACs involving substitution at both ortho positions of the aromatic ring. Multinuclear NMR spectroscopy was used to study the structure of the 1,2-zwitterionic gallium complexes generated and their properties and to examine the mechanisms of the ...

Catalytic cyclopropanation of spiro[2.4]hepta-4,6-diene with diazomethane in the presence of copper or palladium compounds results in mono- and dicyclopropanation products, namely, spiro[bicyclo[3.1.0]hex-3-ene-2,1′-cyclopropane] and spiro[cyclopropane-1,5′-tricyclo[4.1.0.02,4]heptane], with different efficiency. The use of Pd compounds as catalysts allows the cyclopropanation to be performed under conditions of simultaneous generation and decomposition of diazomethane.

A new synthetic concept was suggested in the chemistry of substituted methylidenemalonates that enables their utilization as 1,2-zwitterionic synthons. This strategy is to generate liquid ionic Ga complexes from methylidenemalonates and GaHal3 with a strict 3/4 composition and then use them in further synthesis. A number of complexes with different metal halides have been synthesized and studied in detail. The unique properties of gallium among all metals have been demonstrated and explained. On the basis of the discovered new class of gallium complexes of methylidenemalonates, a number of novel reactions with acetylenes have been elaborated, which are unknown in the conventional chemistry of methylidenemalonates. The main demonstrated process is a three-component addition to a triple bond involving halide anions, leading to the formation of polyfunctional vinyl halides with high E-selectivity. The mechanism has been studied experimentally in fine detail. Application of specially optimized 71Ga NMR spectr...

A new process of "inverted" formal [3 + 2]-cycloaddition of donor-acceptor cyclopropanes (DACs) to allylic systems to give polyfunctionalized cyclopentanes has been developed. Unlike the classical version of formal [3 + 2]-cycloaddition, a DAC acts in this process as a two-carbon synthon (1,2-zwitterionic reactivity type), while an alkene acts as a three-carbon synthon. Tetramethylethylene, allylbenzenes, homoallylbenzene, terminal and internal aliphatic alkenes, and methylenecyclobutane were successfully used as alkenes. Furthermore, in order to suppress annulation at the aromatic ring in 2-arylcyclopropane-1,1-dicarboxylates and enhance the selectivity of the reaction with the allylic system of alkenes, we suggested a new approach for managing the reactivity of DACs involving substitution at both ortho positions of the aromatic ring. Multinuclear NMR spectroscopy was used to study the structure of the 1,2-zwitterionic gallium complexes generated and their properties and to examine the mechanisms of the occurring reactions.

We found, for the first time, that in the presence of HClO4, a slipped-cofacial magnesium J-type phthalocyanine dimer is subjected to demetallation, providing a thermally stable metal-free derivative, as proven by NMR and UV/Vis spectroscopy, as well as by MALDI-TOF mass spectrometry. Our thermoanalytical study demonstrated the high thermal stability of the dimeric ligand (up to 614 °C). The presence of tert-butyl substituents in the dimeric structures allowed us to discover, with the help of field emission scanning electron microscopy (FE-SEM), ordered phases, represented as threads composed of about 200 nm diameter circles, unlike the corresponding monomers, in which similar circles or triangles are scattered randomly. The interaction of the metal-free dimer with magnesium acetate gave an initial dimeric complex with intrinsic spectral properties. Simulation of the optical limiting (OL) properties using the finite field TDDFT (FF-TDDFT) approach (PBE/aug-cc-pVDZ) revealed that the limiting effect for J-type dimers is more pronounced in the visible region, whereas in the near-IR region, at low input fields, they can be used as linear optical filters.

A new process for (4 + 2)-annulation of donor-acceptor cyclopropanes (DACs) with unsaturated compounds in the presence of anhydrous GaCl3 has been developed. In this process, DACs act as sources of formal 1,2- and 1,4-dipoles to give polysubstituted tetralins in high yields and with high regio- and diastereoselectivity. Alkenes with both aryl and alkyl substituents at the double bond undergo this reaction equally readily. A most likely mechanism of the reaction has been proposed. It involves preliminary generation of a key 1,2-dipolar gallium complex and its subsequent participation in annulation with an alkene.

A new original route for the construction of cage structures containing seven electron-withdrawing groups in a molecule is reported. This method is based on the reaction of stable organic cations with a cycloheptatrienyl anion totally substituted with methoxycarbonyl groups. After the formation of a C–C bond between two different carbocycles, some further transformations take place to give cage structures. Reactions of the same cations with N-mesyl-Z-1-[1,2-bis(methoxycarbonyl)-2-(methoxycarbonylamino)ethen-1-yl]-2,3,4,5-tetrakis(methoxycarbonyl)cyclopentadienyl anion affording novel organic salts were also studied.

A new original route to the construction of cage structures containing seven or more electron-withdrawing groups in a molecule was elaborated. This method is based on the reaction of a tropylium cation with a cycloheptatrienyl anion totally substituted with methoxycarbonyl groups. After the formation of a C–C bond between two different seven-membered carbocycles, some further transformations take place to give 2,3,4,5,6,7,8-hepta(methoxycarbonyl)pentacyclo[7.5.0.02.4.03.8.05.14]tetradeca-7,10,12-triene (6). Low temperature NMR experiments for the formation of this compound and some of its reactions were also studied.

Aryldiazomethanes generated by vacuum thermolysis of arenecarbaldehyde tosylhydrazone sodium salts react stereospecifically with 16-dehydropregnenolone acetate. Subsequent decomposition of the pyrazoline adducts yielded hitherto unknown substituted [16α,17α]-cyclopropaprogesterones bearing the aryl substituents at the position 3′. Interaction of such cyclopropaprogesterones with progesterone receptor from rat uterine cytosol was studied.

Novel bi-, tri- and tetranuclear butyl- and tert-butyl-substituted clamshell-type phthalocyanines were synthesized starting from 2-hydroxyphthalocyanines with quantitative yields. The structures of the obtained compounds were characterized by a complex of NMR spectroscopy and mass spectrometry techniques. Applying electronic absorption spectroscopy (UV-vis) and density functional theory (DFT) showed the complicated conformation equilibria for the spacer-bonded macrocyclic compounds and led us to estimate their behavior dependent on the number and relative orientation of macrocycles.

Reactions of alanto-, isoalanto-, and alloalantolactones, which are unsaturated eudesmane-type lactones, with diazocyclopropane generated in situ from N-cyclopropyl-N-nitrosourea under the action of sodium methoxide proceed alike, are highly regio- and stereoselective, and always give spiro-fused pyrazolines via cycloaddition to the exocyclic double bond of the methylidene group of the lactone ring. Their thermolysis at 195–210 °C results in elimination of molecular nitrogen, mainly yielding spiropentane-containing lactones. Minor thermolysis products (10–12%) are isomeric 13-cyclopropyl lactones.

A new method for the synthesis of (1R,4S,5S)-4-hydroxymethyl-3-oxabicyclo[3.1.0]hexan2-one, the cyclopropane analog of (S)-5-hydroxypent-2-en-4-olide, has been suggested based on oxidation of (1S,2S,4R,6R)-7,9-dioxatricyclo[4.2.1.02,4]nonan-5-one. Oxidation of cyclobutanones, spirojoined with the fragments of 6,8-dioxabicyclo[3.2.1]oct-2-ene, 6,8-dioxabicyclo[3.2.1]octane (at position 4), or 7,9-dioxatricyclo[4.2.1.02,4]nonane (at position 5), upon the action of m-chloroperoxybenzoic acid or the KMnO4-H2SO4-H2O system leads to the corresponding spirojoined butanolides in 73–85% yields. The same cyclobutanones easily undergo the four-membered ring opening upon the action of dilute H2SO4 at 50–90 °C to form 6,8-dioxabicyclo[3.2.1]octane-4- or 7,9-dioxatricyclo[4.2.1.02,4]nonane-5-propionic acid.

Diazocyclopropane attacks the carbonyl group of 6,8-dioxabicyclo[3.2.1]octan-4-one or 7,9-dioxatricyclo[4.2.1.02,4]nonan-5-one, saturated derivatives of levoglucosenone, to form the corresponding stereoisomeric oxaspiropentanes. In the case of the strained tricyclononane, 5R-isomer isomerizes under the reaction conditions into spiro-fused cyclobutanone. For this ketone, the formation of homologation products, i.e., the respective regioisomeric spiro-[8,10-dioxatricyclo[5.2.1.02,4]decane-6(5),1′-cyclopropan]-5(6)-ones, is also observed.

Depending of the reaction conditions, reaction of levoglucosenone with diazocyclopropane generated in situ from N-cyclopropyl- N-nitrosourea under the action of bases involved either the carbonyl group to give oxaspiropentane (MeONa/MeOH, s-30 °C), or the double C=C bond to give l-pyrazoline (K2CO3, CH2Cl2, 5 °C). The latter readily reacted with diazocyclopropane at the C=O group or added as a C-nucleophile in a regio-and stereoselective Michael reaction to the C=C bond of levoglucosenone. The direction of reaction depended on the reactant ratio. The reaction of the levoglucosenone—diazomethane adduct with an excess of levoglucosenone in the presence of a base yielded similar product bearing two levoglucosenone moieties.

The reaction of levoglucosenone with methyl diazoacetate gives first 1-pyrazoline, which then, depending on the reaction conditions, either undergoes denitrogenation to form a mixture of cyclopropane and unsaturated compounds, or isomerizes into 2-pyrazoline capable of easy cyclodimerizing in the presence of pyridine through the addition of the N—H fragments to the carbonyl groups. The product of levoglucosenone reduction, 6,8-dioxabicyclo [3.2.1]oct-2-en-4-ol, affords the corresponding cyclopropane upon the action of diazomethane in the presence of a Pd catalyst, whereas its reaction with methyl diazoacetate in the presence of Rh2(OAc)4 leads to the insertion of methoxycarbonyl carbene into the OH bond. From the ester obtained, l-diazo-3-6,8-dioxabicyclo[3.2.1]oct-2-en-4-yloxypropan-2-one was synthesized in several steps, its denitrogenation under the action of copper compounds is accompanied by the intramolecular insertion of the carbene into the C(4)—H bond of the levoglucosenone fragment to yield the corresponding spirane.

3-Aminopyrrolidin-2-ones containing a fused norbornane or spirocyclopropane fragment react with benzaldehyde to give azomethines, which can be transformed into N-substituted 3-aminopyrrolidin-2-ones by reduction with sodium borohydride. Diazotization of amino-pyrrolidinones with NaNO2 in acetic acid results in the elimination of molecular nitrogen and in the formation of acetoxy or unsaturated derivatives (through stabilization of intermediate carbocations). 6-Methylidene4-azaspiro[2.4]heptan-5-one obtained by diazotization of 6-amino-6-methyl-4-azaspiro[2.4]heptan-5-one easily reacts with diazomethane, diazocyclo-propane, and benzonitrile oxide to yield heterocyclic spiranes by means of 1,3-dipolar cycloaddition.

A reaction of cyclopropanediazonium ion, generated by decomposition of N-cyclopropyl-N-nitrosourea upon treatment with potassium or cesium carbonates, with various poly-hydroxyarenes and aminophenols has been studied. The reaction of azo-coupling proceeds with phloroglucinol, resorcinol, 3-methoxy- and 3-aminophenol giving rise to mono-, bis-, and tris(cyclopropylazo)arenes as the major products. Oxidizable phenols such as hydro-quinone, 2-methoxy-, 4-amino-, and 2-aminophenol give products of radical transformations with participation of cyclopropyl radical.

In this new process donor-acceptor cyclopropanes act as sources of formal 1,2- and 1,4-dipoles to afford polysubstituted tetralins in a regio- and diastereoselective manner.

The selective synthesis of heteroleptic (heteronuclear) sandwich-type lanthanide phthalocyanines has been accomplished. Double-decker complexes BuPcLnPc, and BuPcLnPcCl (Ln = Lu, Eu; BuPc = 2,3,9,10,16,17,23,24-octabutylphthalocyaninate; Pc = phthalocyaninate, ClPc = 2,3,9,10,16,17,23,24-octachlorophthalocyaninate) were obtained in good yields by a direct interaction of metal-free ligand BuPcH2 with the monophthalocyanines PcLnOAc or ClPcLnOAc. Heteronuclear triple-decker phthalocyanines PcEuRPcLuRPc, ClPcEuRPcLuRPc and BuPcEuRPcLuRPc (RPc = BuPc, tBuPc; tBuPc = 2(3),9(10),16(17),23(24)-tetra-tert-butylphthalocyaninate) were obtained from the corresponding mono-(PcEuOAc, ClPcEuOAc, BuPcEuOAc) and bisphthalocyanines (RPc2Lu) under similar conditions.

A new way of generating cyclopropyl radicals in the base-catalyzed decomposition of N-cyclopropyl-N-nitrosourea in the presence of organic reducing agents (1-phenylpyrazolidin-3-one and 4-methoxyphenol) was developed. The cyclopropyl radical generated under these conditions can not only abstract a proton from the substrate to give cyclopropane but also form C-C or C-Br bonds in reactions with aromatic substrates or polybromomethanes.

Methods for the selective synthesis of mono-(RPcLnOAc), di-(RPc2Ln), and triphthalocyanines (RPc3Ln2) of rare-earth metals (Ln = Lu, Er, Eu) from symmetrically substituted 2,3,9,10,16,17,23,24-octaalkylphthalocyanines RPcH2 (R = Et, Bu) were developed. The synthesized complexes were characterized by NMR spectroscopy, mass spectrometry, and electronic absorption spectra. The conditions for 1H NMR spectra recording were optimized. Regularities in changing the spectral properties of the synthesized compounds, depending on the lanthanide nature and the planarity of metal phthalocyanine complexes, were found.

The 1,3-dipolar cycloaddition of diazocyclopropane generated in situ to cyclooctyne at –30 to –25 °C afforded highly reactive spiro(9,10-diazabicyclo[6.3.0]undeca-1(8),9-diene-11,1’-cyclopropane) which can add nucleophiles to the azocyclopropane fragment or undergo oligomerization with three-membered ring opening.

Treatment of 1,1-di- and 1,1,1-trifluoroalkane-2,4-diones 10−13 with cyclopropyldiazonium intermediates 2 and 3, generated in situ through the decomposition of N-cyclopropyl-N-nitrosourea 1 by treatment with moist K2CO3, did not result in the expected azo coupling of the cyclopropyldiazonium ion, but afforded the corresponding oxaspiropentanes 14−17 as products of the addition of diazocyclopropane (3) onto one of the carbonyl groups. In addition, the reaction proceeded selectively on the carbonyl groups adjacent to the di- or trifluoromethyl substituents. 1,1-Difluoroacetone reacted analogously with diazocyclopropane (3) generated in situ, giving stable 2-(difluoromethyl)-2-methyloxaspiropentane in approximately 50% yield. The resulting oxaspiropentanes 14−17, on heating or in the presence of lithium iodide, rearranged selectively into cyclobutanones 20−23, while in the presence of Al2O3 they formed mixtures of approximately equal amounts of the corresponding cyclobutanones and the 1-vinylcyclopropanols 24−27. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

New hexadecaalkyl-substituted diphthalocyanine complexes of lanthanides RPc2Ln (R = Et, or Bu; Ln = Lu, Dy, or Eu) were synthesized by three methods: in solution in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene, in a melt of a mixture of the reagents, and under microwave irradiation. The first of the above-mentioned procedures has an advantage for the preparation of Dy and Eu diphthalocyanines, whereas the melt synthesis is a method of choice for the preparation of Lu complexes. The reaction time decreases in going from the first to the third method. The structures of the complexes were confirmed by mass spectrometry, NMR spectroscopy, and electronic absorption spectroscopy.

Thermal, photolytic, and thermocatalytic decomposition of methyl diazoacetate (MDA) in the presence of Rh2(OAc)4 or Cu(acac)2 in refluxing pyridine afforded isomeric trans,cis- and cis,trans-3,4,5,6-tetra(methoxycarbonyl)-1,4,5,6-tetrahydropyridazines (∼1 : 1) in a total yield of 30—70%. Decomposition of MDA in refluxing o-xylene in the presence of Rh2(OAc)4 and pyridine (20 mol.%) gave rise to 2,3,4,5-tetra(methoxycarbonyl)pyrrole in a yield of up to 40%. In these transformations of MDA, neither dimethyl fumarate (or dimethyl maleate) nor the corresponding 2-pyrazolines were generated as intermediates.

The reaction outcome between 2-(het)arylcyclopropane-1,1-dicarboxylates and 1- and 2-pyrazolinecarboxylates in the presence of GaCl3 is temperature-dependent: at 5°C 1:1 adducts are formed, whereas at 40°C 2:1 adducts would predominate.

Decomposition of N-cyclopropyl-N-nitrosourea with bases in the absence of agents for trapping of diazocyclopropane and cyclopropyldiazonium leads to 1,5- and 2,5-disubstituted tetrazoles.

The reactions of diazomethane and diazocyclopropane generated in situ with 1,1,2,2-tetrafluoro-3-vinylcyclobutane (1) and 2,3,3-trifluoro-1-vinylcyclobutene (2) proceeded at the double bond of the substituent as the 1,3-dipolar cycloaddition to form the corresponding 1-pyrazolines. Under the conditions of thermolysis (340—400 °C), the resulting cyclobutylpyrazolines 4 and 5 selectively lost the dinitrogen molecule to generate 3-cyclopropyl-1,1,2,2-tetrafluorocyclobutane (6) or 1,1,2,2-tetrafluoro-3-spiropentylcyclobutane (7), respectively, in high yields. In the presence of Pd(acac)2, the reactions of these fluorine-containing unsaturated compounds and 2-chloro-1,1,2-trifluoro-3-vinylcyclobutane (3) with diazomethane gave rise directly to cyclopropane derivatives 6, 11, and 12, respectively. The reactions of compounds 1 and 2 with methyl diazoacetate in the presence of Rh2(OAc)4 proceeded analogously to yield cis- and trans-disubstituted cyclopropanes.

The addition of the phthalimidonitrene fragment, resulting from oxidation ofN-aminophthalimide by lead tetraacetate at −20 to −30°C, to the N=N-bond of 5-bromospirol[l-pyrazolinio-3,1′-cyclopropane] (1) affords, apart from the stable 5-bromo-N {spiro[l-pyrazolinio-3,1′-cyclopropane]}-N-phthalimidoamide (azimine2), regioisomeric azimine3, which is completely transformed into 3-acetoxy-N-{spiro[l-pyrazolinio-5,1′-cyclopropane]}-N-phthalimidoamide (4) under the reaction conditions. The acetoxy group in this product easily undergoes nuclcophilic substitution on treatment with McOH, NaN3, or the starting bromopyrazoline1. The structures of azimines obtained were established using NMR spectra, and the structure of the product of reaction of4 with1 was additionally proved by X-ray difraction data.

Hydrochlorination of spiro(1-pyrazoline-3,1′-cyclopropanes) proceeds regioselectively at the azocyclopropane group to form 3-(2-haloethyl)pyrazoline derivatives. If the latter contain a halogen atom in the heterocycle, they are readily converted into (2-haloethyl)pyrazole hydrohalides. Bromination of 3-cyanospiro(2-pyrazoline-5,1′-cyclopropane) withN-bromosuccinimide at 20°C proceeds with retention of the cyclopropane ring to form 3-bromo-3-cyanospiro(1-pyrazoline-5,1′-cyclopropane), which is converted into (2-bromoethyl)cyanopyrazole in ∼60% yield at ∼20°C after 3–4 days.

Oxidation ofN-aminophthalimide with lead tetraacetate in the presence of spiro(1-pyrazolinecyclopropanes) at temperature from −20°C to −30°C resulted in the formal generation of phthalimidonitrene followed by its addition at the N=N bond of the pyrazoline ring to form 5(3)-substitutedN-{spiro[1-pyrazolinio-3(5),1′-cyclopropane]}-N-phthalimidoamides (azimines), whose regioisomeric compositions were determined to a large extent by the nature of the substituents in the pyrazoline ring. The structures of phthalimidoazimines were established based on the NMR spectra and X-ray diffraction data. Thermal conversions of the resulting adducts, which proceeded either with retention or with opening of the spiro-fused cyclopropane ring, were studied.

1,3-Dipolar cycloaddition of diazocyclopropane, generated in situ from nitrosourea (I), to cyclooctyne affords the highly reactive spiro-compound (III), which can add nucleophiles to the cyclopropane fragment.

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-diazabicyclo[3. 1 .0] hex-2-ene-4,1 ′-cyclopropanes), in yields of about 70%

Polycyclic spiro(1-pyrazoline-3,1′-cyclopropanes) were obtained in 32–70 % yields by the reaction of diazocyclopropane generatedin situ with 2-methyltricyclo[3.2.1.02,4]oct-6-ene, spiro[2,4]hepta-4,6-diene dimer, benzvalene, spiro[2,3]hex-1-ene, methyl 1-methylcyclopropene-3-carboxylate, buta-1,3-diene, and 2-methylbuta-1,3-diene.

The reaction of 2-(het)arylcyclopropane-1,1-dicarboxylates (I) with 1- and 2-pyrazolinecarboxylates in the presence of GaCl3 affords predominantly 1:1 or 2:1 adducts depending mainly on the reaction temperature.

1-Pyrazolines1–4, which contain a spiro cyclopropane fragment at the adjacent azo group, react selectively with acetyl (benzoyl) chloride or acetic anhydride in the presence of AlCl3 to give high yields of the corresponding 1-acyl-3-(2-chloroethyl)-2-pyrazolines5–8, adducts of electrophilic 1,5-addition of acyl chlorides to the conjugated azocyclopropane system.

1-Pyrazolines1 and2 obtained by 1,3-dipolar cycloaddition of diazocyclopropane to norbornene or deltacyclene undergo dediazotization at 410–450°C to give a mixture of strained hydrocarbons, namely, spirocyclopropane-1,3'-tricyclo[3.2.1.02,4]octane (4) or spiro{cyclopropane-1,4'-pentacyclo[4.4.0.02,8.03,5.07,9]decane} (6) and isomeric tricyclo[5.2.1.02,5]dec-5-enes (5) or pentacyclo[6.4.0.02,10.03,6.09,11]dec-6-enes (7) in a 30–70% overall yield. An increase in temperature favors the isomerization of spiro hydrocarbons4 and6 to the respective unsaturated hydrocarbons5 and7. The latter undergo cyclopropanation with diazomethane in the presence of Pd(acac)2 or (PhO)3P · CuCl to afford polycyclanes9a,b or10a,b containing a spiro[2.3]hexane moiety condensed at thecis-1,4 position. Unsaturated 1-pyrazoline3 obtained from diazocyclopropane and norbornadiene decomposes at 330–370°C with elimination of cyclopentadiene to give 3(5)-vinylpyrazole in a yield up to 75%.

The formation of the novel hydrocarbons, tetracyclo[7.2.1.02,5.02,8]dodecadienes, as a result of thermal isomerization of spiro[2.4]hepta-4,6-diene into bicyclo[3.2.0]hepta-1,3-diene and its capture by 1,3-dienes is demonstrated. The conditions of thermal isomerization and dimerization of the spiroheptadiene are studied. Cyclopropanation of the polycyclic dienes formed by diazomethane in the presence of Pd-catalysts was accomplished, and occured solely through the norbornene double bond.