Regio‐ and stereospecific assembly of dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidines] from simple precursors using a one‐pot procedure: synthesis,spectroscopic and structural characterization,and a proposed mechanism of formation

The synthesis and characterization of three new dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine] compounds are reported, together with the crystal structures of two of them. (3RS,1′SR,2′SR,7a′SR)‐2′‐(4‐Chlorophenyl)‐1‐hexyl‐2′′‐sulfanylidene‐5′,6′,7′,7a′‐tetrahydro‐2′H‐dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine]‐2,4′′‐dione, C₂₈H₃₀ClN₃O₂S₂, (I), (3RS,1′SR,2′SR,7a′SR)‐2′‐(4‐chlorophenyl)‐1‐benzyl‐5‐methyl‐2′′‐sulfanylidene‐5′,6′,7′,7a′‐tetrahydro‐2′H‐dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine]‐2,4′′‐dione, C₃₀H₂₆ClN₃O₂S₂, (II), and (3RS,1′SR,2′SR,7a′SR)‐2′‐(4‐chlorophenyl)‐5‐fluoro‐2′′‐sulfanylidene‐5′,6′,7′,7a′‐tetrahydro‐2′H‐dispiro[indoline‐3,3′‐pyrrolizine‐1′,5′′‐thiazolidine]‐2,4′′‐dione, C₂₂H₁₇ClFN₃O₂S₂, (III), were each isolated as a single regioisomer using a one‐pot reaction involving l ‐proline, a substituted isatin and (Z)‐5‐(4‐chlorobenzylidene)‐2‐sulfanylidenethiazolidin‐4‐one [5‐(4‐chlorobenzylidene)rhodanine]. The compositions of (I)–(III) were established by elemental analysis, complemented by high‐resolution mass spectrometry in the case of (I); their constitutions, including the definition of the regiochemistry, were established using NMR spectroscopy, and the relative configurations at the four stereogenic centres were established using single‐crystal X‐ray structure analysis. A possible reaction mechanism for the formation of (I)–(III) is proposed, based on the detailed stereochemistry. The molecules of (I) are linked into simple chains by a single N—H…N hydrogen bond, those of (II) are linked into a chain of rings by a combination of N—H…O and C—H…S=C hydrogen bonds, and those of (III) are linked into sheets by a combination of N—H…N and N—H…S=C hydrogen bonds.     

The synthesis of novel polycyclic heterocyclic ring systems via photocyclization. 6. Naphthothienonaphthyridines

Five novel polycyclic heterocyclic ring systems are reported via photocyclization. The specific final products in these ring systems are: naphtho[1′,2′:4,5]thieno[2,3-c][1,8]naphthyridin-6(5H)-one ( 5 ), naphtho-[1′,2′:4,5]thieno[2,3-c][1,6]naphthyridin-6(5H)-one ( 6 ), naphtho[1′,2′:4,5]thieno[2,3-c]-1,5-naphthyridine ( 9 ), naphtho[1′,2′:4,5]thieno[2,3-c][1,2,4]triazolo[4,3-a]-1,5-naphthyridine ( 12 ), and naphtho[2′,1′:4,5]thieno[2,3-c]-1,5-naphthyridine ( 17 ). The direction of photocyclization to produce 9 was established from a zero quantum two-dimensional nmr spectroscopy experiment (ZQCOSY) using 6-chloronaphtho[1′,2′:4,5]thieno[2,3-c]-1,5-naphthyridine ( 8 ) as the model compound.     

The photochemical synthesis of novel heterocyclic compounds from s-triazolo [4,3-b] pyridazine,III

s-Triazolo[4,3-b]pyridazine (I) reacted photochemieally with bieyélo[2.2.1] hepla-2,5-diene, 1,5-cyclooctadiene, 1,3-cyclooctadiene, methylene cyclohexane, diethyl cis-1,2,3,6-tetrahydro-phthalate and ethyl 2-cyclopentene-1-acetate to givt: the following products: the endo and exo isomers of 4a, 5, 8a, 9-tetrahydro-9-rnethylene-5,8-rnethano-8H-s-triuzolo[1, 5-a]indole (II) and the endo and exo-9-cyanometliyl products (III and IV) from bicyclo[2.2.1] hepta-2,5-diene; 4a,5,-9, 10, 10a, 11-huxahydro-11-methylene-6H-cycloocta[4,5]pyrrolo[1,2-b]-s-triazole (V) and the 11-cyanomethyl product VI from 1,5-cyclooctadiene: 4a,7,8,9,10,10a-hexahydro-11 -inethylene-11H-cycloocta[4,5]pyrrolo[1,2-b]-s-triazole(VII),4a, 5, 7, 8, 10a, 11-hexahydro-11-methylene-6H-cycloocta[4,5]pyrroIo[1,2-b]-s-triazole (VIII) and their respective 9-cyanomethyl products (X and 1X) from 1,3-cyclooctadiene; 6′, 7′ -dihydro-7′ -methylenespiro[cyclohexane-1, 5′-[5H] pyr-rolo[1,2-b]-s-triazole] (XI), 6′, 7′-dihydro-7′-meth) lene. spiro cyclohexane-1, 6′-[5H]pyrrolo[1,2-b]-s-triazole] (XII) and their respective 7 -eyanomethyl products (XIII and XIV) from melhylene cyclohexane; 6,7-dicarbethoxy-9-cyanomelhyl-4a, 5, 7, 8, 8a, 9-hexahydro-6H-s-triazolo[1,5-a]indole (XV) from diethyl cis-1, 2, 3, 6-tetrahydrophlhalate: and 5-earl)elhoxymethyl-8-eyanomethyl-4a, 5, 6, 7, 7a, 8-hexahydrocyclopenta[4,5]pyrrolo( 1, 2-b]-s-triazole (XVI) from ethyl 2, 2-cyclo-pentene-1-acetate. Many other alkenes, particularly the phenyl ethylenes, did not react with compound 1. In general, more than one product was isolated for each reaction except in the case of the two ester alkenes where a single eyanomethyl product was observed.     

Synthesis of spiro[2H-indole-2,1′-1H-isoindole]-3,3′-diones,spiro[1H-isobenzofuran-1,2′-2H-indole]-3,3′-diones and spiro[benzofuran-2,1′-isobenzofuran]-3,3′-diones via transannular reactions of eight membered ring intermediates

An auto oxidation-rearrangement product 4 was isolated from a high dilution reaction of ninhydrin with 3,4,5-trimethoxyaniline in water. A general synthesis of this compound and its derivatives 4–6 was devised by oxidation of tetrahydroindeno[1,2-b]indol-10-ones 1–3 with sodium periodate to give isoindolo[2,1-a]-indole-6,11-diones 4–6 in good yield. Compounds 4–6 can be easily transformed into spiro[1H-isobenzofuran-1,2′-2H-indole]-3,3′-diones 8–10 , spiro[2H-indole-2,1′-1H-isoindole]-3,3′-diones 11–13 and isoindole[1,2-a:2′,1′-b]pyrimidine-5,15-diones 15, 16 in high yields. Analogous reactions were performed on 3-amino-5a, 10a-dihydroxybenzo[b]indeno[2,1-d]furan-10-one ( 17 ) to give a dibenzoxocintrione 18 , spiro-[benzofuran-2,1′-isobenzofuran]-3,3′-dione 19 and an isoindol-1-one 20 .     

Studies on the synthesis of heterocyclic compounds. Part IV. Further investigation of the pschorr reaction with some pyrazole derivatives

Thermal decomposition of the diazonium sulfate derived from N-methyl-(1-phenyl-3-methylpyrazol-5-yl)-2-aminobenzamide afforded products formulated as 1-phenyl-3-methyl[2]benzopyrano[4,3-c]pyrazol-5-one (yield 10%), 1,4-dimethyl-3-phenylpyrazolo[3,4-c]isoquinolin-5-one (yield 10%), N-methyl-(1-phenyl-3-methylpyrazol-5-yl)-2-hydroxybenzamide (yield 8%) and 4′-hydroxy-2,3′-dimethyl-1′-phenylspiro[isoindoline-1,5′-[2]-pyrazolin]-3-one (yield 20%). Decomposition of the diazonium sulfate derived from N-methyl-(1,3-diphenylpyrazol-5-yl)-2-aminobenzamide gave products formulated as 7,9-dimethyldibenzo[e,g]pyrazolo[1,5-a][1,3]-diazocin-10-(9H)one (yield 8%), 4-methyl-1,3-diphenylpyrazolo[3,4-c]isoquinolin-5-one (yield 7%) and 4′-hydroxy-2-methyl-1′,3′-diphenylspiro[isoindoline-1,5′-[2]pyrazolin]3-one (yield 10%). The spiro compounds 6a,b underwent thermal and acid-catalysed conversion into the hitherto unknown 2-benzopyrano[4,3-c]pyrazole ring system 7a,b in good yield. Analytical and spectral data are presented which supported the structures proposed.     

Synthesis of spiro[furan-3,3′-indolin]-2′-ones by PET-catalyzed [3+2] reactions of spiro[indoline-3,2′-oxiran]-2-ones with electron-rich olefins

An efficient procedure for the synthesis of spiro[furan-3,3′-indolin]-2-ones and dispiro[cycloalkane-1,2′-furan-3′,3″-indolin]-2″-ones has been achieved in high yields and stereoselectivity by photoinduced electron transfer-catalyzed [3+2] reactions of substituted spiro[indoline-3,2′-oxiran]-2-ones with olefins. The reactions proceed by ring opening of spiro[indoline-3,2′-oxiran]-2-ones via C_β–O bond cleavage and subsequent cycloaddition with olefins by using 2,4,6-triphenylpyrylium tetarfluoroborate (TPT) as a sensitizer.     

Automerisierung von 1,3,5,5-Tetramethylcyclohexa-1,3-dien. Vorläufige Mitteilung

1,3,5,5-Tetramethylcyclohexa-1,3-diene, specifically deuterated in all positions except the gem.-dimethyl groups ( 11 ), was synthesized and found to undergo a rearrangement in the gas phase at 560°, which leads to a statistical distribution of the 6 hydrogen atoms to all 16 positions. This shows that the title compound ( 2 ) automerizes under these conditions and that the reaction proceeds via a series of ring openings (to 5 ) followed by degenerate [1,7]-H-shifts and rig closures (back to 2 ) rather than via [1,5]-CH₃-shifts. It is suggested that the previously studied rearrangement of 5,5-dimethylcyclohexa-1,3-diene ( 1 ) to 1,5-dimethylcyclohexa-1,3-diene ( 3 ) takes its course by the same reaction pathway.     

Synthesis of some fused triazoloquinolines

The reaction of 3 -amino-1,2,4-triazolo[4,3-a]quinoline ( II ) with diethyl ethoxymethylenemalonate and ethyl acetoacetate/ethyl trifluoroacetoacetate afforded 10-carboethoxy-9-oxo-9H-pyrimido[1′,2′:1,5][1,2,4]triazolo-[4,3-a]quinoline ( III ) and 11-methyl/trifluoromethyl-9-oxo-9H-pyrimido[1′,2′:1,5][1,2,4]triazolo[4,3-a]quinoline ( IV/V ) respectively. 2-Chloropyridine-3-carboxylic acid chloride reacted with II to yield 5-oxo-5H-pyrido-[3″,2″:5′,6′]pyrimido[1′,2′:1,5][1,2,4]triazolo[4,3-a]quinoline ( VII ), a new ring system.     

NBO and NICS analysis of the allylic rearrangements (the Cope and 3-aza-Cope rearrangements) of hexa-1,5-diene and N-vinylprop-2-en-1-amine: A DFT study

In this work, ab initio density functional theory (DFT) calculations have been performed on the 3,3-sigmatropic rearrangements of hexa-1,5-diene (Cope) and N-vinylprop-2-en-1-amine (3-aza-Cope) in the gas phase. The barrier heights and heats of reactions calculated at the B3LYP/6-311G** level of theory were in good agreement with experimental data. Transition states optimized with B3LYP/6-311G** theory were used for calculating the nucleus independent chemical shift (NICS) and, a natural bond orbital (NBO) analysis was also performed at the same level of theory. Our results indicate that the aromaticities of the transition states are controlled by the out-of-plane component and that the chair-like transition state of the Cope rearrangement exhibits the strongest aromatic character. Analysis of donor-acceptor (bonding and anti-bonding) interactions of σ_3–4 → π*_1–2 suggests that the TS structure in the hexa-1,5-diene reaction (the Cope rearrangement) has more aromatic character than the N-vinylprop-2-en-1-amine reaction (the 3-aza-Cope rearrangement). The NBO results show that in the hexa-1,5-diene and N-vinylprop-2-en-1-amine rearrangements, activation energies are controlled by σ_3–4 → π*_1–2 and σ_3–4 → π*_1–2 resonance energies.      

One‐pot,fast cyclopropanation reaction of indandione with various aldehydes in the presence of cyanogen bromide and trimethylamine

A new, fast, and easy one‐pot cyclopropanation reaction of aromatic and aliphatic aldehydes with 1H‐indene‐1,3(2H)‐dione and cyanogen bromide (BrCN) was developed for synthesizing 3′‐(aryl[alkyl])‐dispiro[indan‐2,1′‐cyclopropane‐2′,2′′‐indan]‐1,1′′,3,3′′‐tetrone in excellent yields in a short time (about 15 s) under basic media. All structures were characterized using IR, ¹H NMR, and ¹³C NMR spectroscopy techniques.     

Sequential [3,3]Sigmatropic Rearrangement: Regioselective Synthesis of Dimedone‐Annulated Heterocycles

The [3,3]sigmatropic rearrangement in the 3‐(4′‐aryloxybut‐2′‐ynyl)mercapto‐5,5‐dimethyl cyclohex‐2‐enones afforded a number of 4‐aryloxymethyl‐7,7‐dimethyl‐6,7,8‐trihydrothiochrom‐3‐en‐5‐ones (70–80%), which underwent second [3,3]sigmatropic rearrangement to furnish benzofuro[3,2‐c][1]‐2,3,4,6,6a,11a‐hexahydro‐3,3,11a‐trimethylthiobenzopyran‐2‐ones (60–70%).     

Synthesis and Properties of Brominated 6,6'-Dimethyl-[2,2'-bi-1H-indene]-3,3'-diethyl-3,3'-dihydroxy-1,1 '-diones

Photochromic 6‐bromomethyl‐6′‐methyl‐[2,2′‐bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 2 ), 6,6′‐ bis(bromomethyl)‐[2,2′‐bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 3 ) and 6,6′‐bis(dibromomethyl)‐[2,2′‐ bi‐1H‐indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 4 ) have been synthesized from 6,6′‐dimethyl‐[2,2′‐bi‐1H‐ indene]‐3,3′‐diethyl‐3,3′‐dihydroxy‐1,1′‐dione ( 1 ). The single crystal of 4 was obtained and its crystal structure was analyzed. The results indicate that in crystal 4 , molecular arrangement is defective tightness compared with its precursor 1 . Besides, UV‐Vis absorption spectra in CH₂Cl₂ solution, photochromic and photomagnetic properties in solid state of 2 , 3 and 4 were also investigated. The results demonstrate that when the hydrogen atoms in the methyl group on the benzene rings of biindenylidenedione were substituted by bromines, its properties could be affected considerably.     

Condensed Isoquinolines. 15. Synthesis of 5,10-Dihydro[1,2,4]triazolo[1,5-b]isoquinolines and Related Spiranes

Condensation of o-bromomethylphenylacetonitrile with arylcarbohydrazides gave, depending on the reaction conditions, 2-arylcarboxamido-1,4-dihydroisoquinoline-3(2H)-imine hydrobromides or 2-aryl-5,10-dihydro[1,2,4]triazolo[1,5-b]isoquinolines. Analogous condensation of 4-(2-bromomethylphenyl)tetrahydro-2H-pyran-4-carbonitrile and 1-(2-bromomethylphenyl)-1-cyclopentanecarbonitrile with arylcarbohydrazides gave respectively 2-aryl-2,3,5,6-tetrahydrospiro[4H-pyran-4,10'(5'H)-[1,2,4]triazolo[1,5-b]isoquinolines and 2-arylspiro[1,2,4]triazolo[1,5,b]isoquinoline-10(5'H)-1'-cyclopentanes, derivatives of new spirane heterocycles. The reaction with condensing agents of 3-imino-2,2',3,3'5',6'-hexahydrospiro[isoquinoline-4(1H),4'-4H-pyran]-2-amine and 3-imino-2,3-dihydrospiro[isoquinoline-4(1H),1'-cyclopentane]-2-amine hydrobromides, synthesized from the corresponding bromo nitriles and hydrazine, may serve as an alternative route for the synthesis of these compounds. The structure of obtained triazoloisoquinolines was established from IR, ¹H and ¹³C NMR spectra. An X-ray crystallographic study of 2-phenylspiro[1,2,4]triazolo[1,5-b]isoquinoline-10(5H),1'-cyclopentane was carried out.     

Ring transformation of 1,5-benzoxazepines into spirobenzoxazoles. Synthesis of pyrazolo[1′,5′:3,4][1,2,4]triazino-[5,6-b][1,5]benzoxazepines and spiro[benzoxazole-2′(3′H),4(1H)-pyrazolo[5,1-c][1,2,4]triazines]

The reactions of the 3-substituted 4-amino-8-ethoxycarbonyl[5,1-c][1,2,4]triazines 1 and 2 with o-amino-phenol hydrochloride gave the pyrazolo[1′,5′:3,4][1,2,4]triazino[5,6-b][1,5]benzoxazepines 5 and 8 . The alkylation of 5 with methyl iodide and isopropyl iodide afforded the 6-alkoxylpyrazolo[1′,5′:3,4][1,2,4]triazino-[5,6-b][1,5]benzoxazepines 6a and 6b , respectively. Refluxing of 5, 6a, 6b and 8 in hydrochloric acid/acetic acid resulted in ring transformation to produce the spiro[benzoxazole-2′(3′H),4(1H)pyrazolo[5,1-c][1,2,4]-triazines] 7a, 7b and 9 . The screening data of the above compounds was described.     

Die konjugative Wechselwirkung zwischen π- und Walsh-Orbitalen: Das Photoelektron-Spektrum des Homofulvens

Analysis of the photoelectron spectrum of homofulvene ( 1 ) (spiro [2.4] hepta-4,6-diene) confirms the conclusions previously drawn concerning the direct conjugation between π-and Walsh-orbitals. It is shown that the resonance integral (4) appropriate for the semi-quantitative interaction of these orbitals amounts to ?1.9 eV, i.e. nearly the value for conjugating π-orbitals (β = ?2.4 to ?2.5 eV). This explains the close analogy between the photoelectron spectrum of 1 and that of fulvene.     

Synthesis,structure, and conformation of terphenylene-derived azacalix[4]aromatics

Several novel azacalix[4]aromatics constituting terphenylene units have been synthesized via sequential nucleophilic aromatic substitution reactions of 5′-t-butyl-(1,1′:3′,1″-terphenyl)-3,3″-diamine 9 and 5′-t-butyl-(1,1′:3′,1″-terphenyl)– 4,4″-diamine 11 with 1,5-difluoro-2,4-dinitrobenzene and cyanuric chloride, respectively. The bridging –NH– functions of the tetra-nitro substituted azacalix[2]arene[2]terphenylenes 1 and 2 have been transformed to the corresponding –N(CH₃)– bridged azacalix[2]arene[2]terphenylenes 3 and 4 via N-alkylation. Single crystal X-ray analysis revealed that the terphenyl-3,3″-diamine derived azacalix[2]terphenylene[2]triazine 5 adopts a distorted chair conformation in the solid state, and the terphenyl-4,4″-diamine derived azacalix[2]terphenylene[2]triazine 6 was found to adopt a 1,3-alternate conformation.     

The Photorearrangements of a Naphthobarrelene-like System. Dependence on excited-state spin multiplicity and electronic configuration,and evidence for biradical intermediates. Preliminary communication

8-Benzoyl-9-deuterio-naphtho [de-2.3.4]bicyclo [3.2.2]nona-2,6,8-triene ( 1 ) rearranged quantitatively in a photochemical di-π-methane-type process to 2-, 6-, and 9-deuteriated 1-benzoyl-naphtho [de-2.3.4]tricyclo [4.3.0.0^2,9]nona-2, 6-diene ( 8a–c ). The phenylhydroxymethyl analogue 2 underwent a similar regioselective rearrangement to 9a–c . The rearrangement 1 → 8a–c is proposed to proceed along three reaction paths evolving from two primary photochemical processes of naphthylvinyl and vinyl-vinyl bonding ( 1 → 3 + 6 ). Evidence for a competition between several paths and involvement of biradical intermediates derives from changes in the isotopomeric composition with temperature, and from laser flash detection (λ_exc 353 nm) of a transient. The dependence of the quantum yield for product formation from 1 on excitation wavelength and sensitizer triplet energy leads to the conclusion that reaction to the primary biradicals occurs directly from the S₁ (n, π*) and T₂ (n, π* ) states, and that reaction from T₁ (π, π*) and from S₂ (π, π*) proceed either directly or via T₂.     

Five-membered 2,3-dioxo heterocycles: XCII. Reaction of 3-aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones with ethyl (2Z)-(3,3-dimethyl-8-oxo-2-azaspiro[4.5]deca-6,9-dien-1-ylidene)ethanoate. Synthesis of bridged analogs of pyrrolizidine alkaloids

3-Aroyl-1H-pyrrolo[2,1-c][1,4]benzoxazine-1,2,4-triones reacted with ethyl (2Z)-(3,3-dimethyl-8-oxo-2-azaspiro[4.5]deca-6,9-dien-1-ylidene)acetate to give ethyl 6′-aryl-2′-(2-hydroxyphenyl)-11′,11′-dimethyl-3′,4,4′,13′-tetraoxospiro[2,5-cyclohexadiene-1,9′-(7′-oxa-2′,12′-diazatetracyclo[6.5.1.0^1,5.0^8,12]tetradec-5′-ene)]-14′-carboxylates whose structure was confirmed by X-ray analysis. The products may be regarded as bridged analogs of pyrrolizidine alkaloids, 7′-oxa-2′,12′-diazatetracyclo[6.5.1.01,5.08,12]tetradecanes.     

Reactions of 2′-oxo-1′,2′-dihydrospiro[cyclopropane-1,3′-indole]-2,2,3,3-tetracarbonitriles with nucleophiles

2′-Oxo-1′,2′-dihydrospiro[cyclopropane-1,3′-indole]-2,2,3,3-tetracarbonitriles reacted with oxygencentered nucleophiles to form addition products at the cyano groups with conservation of the three-membered ring. Reactions of the title compounds with alcohols required the presence of base catalyst, and the products, 2-amino-4,4-dialkoxy-2′-oxo-1′,2′-dihydrospiro[3-azabicyclo[3.1.0]hex-2-ene-6,3′-indole]-1,5-dicarbonitriles, were converted into the corresponding 2-imino-2′,4-dioxospiro[3-azabicyclo[3.1.0]hexane-6,3′-indole]-1,5-dicarbonitriles and 2,2′,4-trioxospiro[3-azabicyclo[3.1.0]hexane-6,3′-indole]-1,5-dicarbonitriles by the action of acetic and sulfuric acids, respectively. The reactions with ketone oximes occurred in the absence of a catalyst, yielding 2-amino-4,4-bis(alkylideneaminooxy)-2′-oxo-1′,2′-dihydrospiro[3-azabicyclo[3.1.0]hex-2-ene-6,3′-indole]-1,5-dicarbonitriles. The reactions with thiols, aliphatic amines, and anilines were accompanied by opening of the three-membered ring. In the reactions with triphenylphosphine and thiols 2-(2-oxo-2,3-dihydro-1H-indol-3-ylidene)malononitrile was obtained, while morpholine and N,N-dimethylaniline gave rise, respectively, to 3,3-diaryl-and 3,3-dimorpholino-1H-indol-2(3H)-ones and tri- and dicyanoethylene derivatives.     

Synthesis of nitrogen-containing heterocycles. 8. Preparation and ring-opening of spiro[cycloalkane-[1′,2′,4′]triazolo[1′,5′-c]pyrimidine] derivatives

Diaminomethylene- and aminomethylthiomethylenehydrazones [2] of cyclic ketones 1–8 readily reacted with ethoxymethylenemalononitrile to give spiro[cycloalkane-1,2′-[1,2′,4′]triazolo[1,5′-c]pyrimidine-8′-carbonitrile] derivatives 12–19 through the electrocyclic reaction of the initially formed condensation products 26 in moderate to high yields. The spiro[cyclopentanetriazolopyrimidine] derivatives underwent ring-opening at the cycloalkane moiety upon heating in solution to give 2-alkyl-5-substituted-[1,2,4]triazolo[1,5-c]pyrimidine-8′-carbonitriles 20–23 . When an alkyl substituent was introduced into the cyclopentane ring, cleavage of the spiro compounds occurred preferentially at the cyclopentane moiety between the spiro carbon and the more branched one. In contrast, the cyclohexane ring, especially of spiro-5-amino-triazolopyrimidines 17 and 18 strongly resisted to ring-opening under similar conditions, but those of 5-methylthiotriazolopyrimidines 14 gave up to 17 percent of cleavage after prolonged heating in hot ethanol. 2-t-Butyl-5-methylthio-2,3-dihydro[1,2,4]triazolo[1,5-c]pyrimidine-8-carbonitrile 25 [R³ = C(CH₃)₃] was highly susceptible to the cleavage even at room temperature and produced the corresponding 2-unsubstituted triazolopyrimidine 24 with loss of the t-butyl group.