Preparation of 5-substituted- and 3,5-disubstituted-s-triazolo[4,3-a]pyridines

Cyclization of N-acyl-N′-(6-chloropyrid-2-yl)hydrazines ( 2a-2e ) with phosphorus oxychloride has produced several 5-chloro-s-triazolo[4,3-a]pyridines ( 3a-3e ). Nucleophilic displacement of the chlorosubstituent of 5-chloro-s-triazolo[4,3-a]pyridine ( 3a ) availed the 5-ethoxy ( 4a ) and 5-thioethoxy ( 4b ) derivatives and di(s-triazolo[4,3-a]pyrid-5-yl)sulfide ( 8 ) while reaction of 5-ethylsulfonyl-s-triazolo[4,3-a]pyridine ( 4d ) with potassium hydroxide yielded the 5-hydroxy/5-one system ( 4c or 6 ). Further reaction of 3a with bromine to give 3-bromo-5-chloro-s-triazolo-[4,3-a]pyridine ( 3g ) has provided the corresponding 3-cyano- and 3-carboxamido-5-chloro-s-triazolo[4,3-a]pyridine derivatives ( 3h and 3i ). Treatment of 6-chloro-2-hydrazinopyridine ( 1 ) with cyanogen bromide has provided 3-amino-5-chloro-s-triazolo[4,3-a]pyridine ( 3f ) which, with bromoacetaldehyde dimethyl acetal, transformed into 7-chloroimidazo[1,2-b]-s-triazolo[4,3-a]-pyridine ( 7 ). Finally, attempts at cyclizing N-oxalyl-N′-(6-chloropyrid-2-yl)hydrazine derivatives ( 2g-2i ) with intentions of preparing various 3-acyl-5-chloro-s-triazolo[4,3-a]pyridines for entry into other 3,5-disubstituted systems were unsuccessful.     

The synthesis of novel polycyclic heterocyclic ring systems via photocyclization. 8 . [1]Benzothieno[2,3-c]naphtho[1,2-h]quinoline and [1]benzothieno[2,3-c]naphtho[1,2-h][1,2,4]triazolo[4,3-a]quinoline

The previously unknown polycyclic heterocyclic ring systems, namely, [1]benzothieno[2,3-c]naphtho[1,2-h]-quinoline and [1]benzothieno[2,3-c]naphtho[1,2-h][1,2,4]triazolo[4,3-a]quinoline were synthesized via photocyclization of 3-chloro-N-(1′-phenanthryl)benzo[b]thiophene-2-carboxamide.     

A facile synthesis of pyrrolo[1,2-a]pyrimidines and pyrrolo[1,2-a]imidazoles

The one-step synthesis of 8-t-butoxycarbonyl-6,7-dimethyl-2-oxo-1,2,3,4-tetrahydropyrrolo[1,2-a]pyrimidine from acetyl methyl carbinol, 3-aminopropionic acid, and t-butyl cyanoacetate is reported. Utilizing a similar technology under basic conditions, 7-substituted 5,6-dimethyl-2-oxo-2,3-dihydro-(1H)-pyrrolo[1,2-a]imidazole is synthesized from acetyl methyl carbinol, ethyl glycinate, and the appropriate acetonitrile.     

A new synthesis of imidazo[1,2-a]pyridine and imidazo[2,1-a]isoquinoline derivatives

A new synthesis of imidazo[1,2-a]pyridine and imidazo[2,1-a]isoquinoline derivatives 4 and 8 , respectively by 1,5-dipolar cyclization reactions of stabilized pyridinium N-ylides 3a-e or isoquinolinium N-ylide 7 is described. The starting N-ylides 3a-e and 7 are prepared by the reaction of the corresponding pyridinium salts 1a-e or isoquinolinium salts 6 with N-bis(methylthio)methylene-p-toluenesulfonamide (2) .     

Synthesis of 5H-benzimidazo[1,2-a][1,3,4]thiadiazolo[2,3-d][1,3,5]triazin-5-one and 12H-benzimidazo[1,2-a]pyrimido[6,1-d][1,3,5]triazin-12-one,two new heterocyclic ring systems

2-(2,6-Dimethylpyrimidin-4-ylaminobenzimidazole) (VIIa) and 2-(1,3,4-thiadiazol-2-ylamino)benzimidazole (VIIb) underwent a ring-closure reaction with phosgene giving 1,3-dimethyl-12H-benzirnidazo[1,2-a]pyrirnido[6,1][-d][1,3,5]triazin-12-one (IIa) and 5H-benzimidazo[1,2-a][1,3,4]thiadiazolo[2,3-d][1,3,5]triazin-5-one (IIb) two hitherto unknown heterocyclic systems. A convenient synthesis of 2,6-dimethyl-4-aminopyrimidine is described.     

Synthesis and reactions of ethyl 3-acetyl-8-cyano-6,7-dimethylpyrrolo[1,2-a]pyrimidine-4-carboxylate and related compounds

The reactions of 3-acetyl-4-ethoxycarbonyl- or 3,4-diethoxycarbonylpyrrolo[1,2-a]pyrimidine derivatives 7a,b , which were prepared by condensation of the 2-aminopyrrole ( 4 ) with ethyl 3-ethoxymethylene-2,4-dioxovalerate ( 5a ) or ethyl ethoxymethyleneoxaloacetate ( 5b ), with diazomethane are described. Thus, reaction of 7a , with diazomethane gave ethyl 2a-acetyl-7-cyano-2a,3a-dihydro-5,6-dimethyl-3H -cyclopropa[e]pyrrolo[1,2-a]pyrimidine-3a-carboxylate ( 11 ) in 74% yield, which was readily transformed into the 1-pyrrol-2-yl-pyrrole ( 18 ) by treatment with potassium hydroxide. On the other hand, reaction of 7b with diazomethane afforded three products whose structures were assigned as diethyl 7-cyano-2a,3a-dihydro-5,6-dimethyl-3H-cyclopropa[e]pyrrolo[1,2-a]pyrimidine-2a,3a-carboxylate ( 20 ), 6-cyano-7,8-dimethyl-3a,3b,5,9a-tetrahydro-4H -aziridino[c]-1H or 3H-pyrazolo[3,4-e]pyrrolo[1,2-a]pyrimidine-3a,9a-dicarboxylates ( 21,22 ). Ring Transformation of 20 to 25 was not observed.     

Fused Polycyclic Nitrogen-Containing Heterocycles: VI. Pyrrolo[1,2-a]quinoxalines

3-(-Chlorobenzyl)-1,2-dihydroquinoxalin-2-one reacts with anions derived from acetylacetone, benzoylacetone, dibenzoylmethane, malononitrile, ethyl acetoacetate, and ethyl cyanoacetate to give the corresponding 3-(-R,R'CH-benzyl)-1,2-dihydroquinoxalin-2-ones which undergo intramolecular cyclocondensation to functionally substituted pyrrolo[1,2-a]quinoxalines on heating in boiling acetic acid. The reaction of 3-(-chloro-p-nitrobenzyl)-1,2-dihydroquinoxalin-2-one with acetylacetone anion directly leads to the corresponding pyrrolo[1,2-a]quinoxaline, without heating in acetic acid.     

Fused s-triazino heterocycles. XVII. 8,13-Dihydro-1,3,7,8,13c-pentaazabenzo[de]naphthacene, 7H-1,3,7,8,11b,12,14-heptaazadibenzo[de,hi]naphthacene and 8H-1,3,7,8,13,14c-hexaazabenzo[4,5]cyclohepta[1,2-a]phenalene,three new ring systems

The reaction of 7,9-dibromo-5-tribromornethyl-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene ( 1a ) with p-toluidine is shown to give 4,6-dibromo-2-t-butyl-8,13-dihydro-13-imino-11-methyl-1,3,7,8,13c-pentaazabenzo[de]naphthacene ( 4 ) in two steps with 7,9 dibromo-2-t-butyl-4-cyano-5-p-toluidino-1,3,6,9b-tetraazaphenalene ( 2b ) as the intermediate product. A related annulation reaction of 1a with N-(5-amino-2,4-dimethylphenyl)trimethylacetamide ( 8 ) leads in two steps to 9,11-dibromo-2,13-di-t-butyl-4,6-dimethyl-7H-1,3,7,8,11b,12,14-heptaazadibenzo[de,hi]naphthacene ( 6 ) with 7,9-dibromo-2-t-butyl-4-cyano-5N-(2,4-dimethyl-5-trimethylacetamidophenyl)amino-1,3,6,9b-tetraazaphenalene ( 2d ) as the intermediate product. In a similar fashion the reaction of 1a with o-phenylenediamine forms 14-amino-4,6-dibromo-2-t-butyl-8H-1,3,7,8,13,14c-hexaazobenzo[4,5]cyclohepta[1,2-a]-phenalene ( 12 ) by way of the intermediate 5-N-(2-aminophenyl)amino-7,9-dibromo-2-t-butyl-4-cyano-1,3,6,9b-tetraazaphenalene ( 2e ). The preparation of N-(2,4-dimethyl-5-nitrophenyl)-trimethylacetamide ( 11 ) and its reduction to N-(5-amino-2,4-dimethylphenyl)trimethylacetamide ( 8 ) is also described.     

Carbon-nitrogen bond formation in cyclisation by deoxygenation,thermolysis or photolysis of phenylimidazo[1,2-a][1,8]naphthyridines

Triethyl phosphite deoxygenation of 2-(2-nitrophenyl)imidazo[1,2-a][1,8]naphthyridine (3) led to the C-insertion to give the indoloimidazonaphthyridine 5. Our attempt to promote the N-insertion by blocking the C-3 position failed. Triethyl phosphite deoxygenation of 1-nitroso-2-(4-fluorophenyl)imidazo[1,2-a][1,8]-naphthyridine (12) led to the corresponding amine structure (15). Thermolysis and photolysis of 6,8-dimethyl-2-(2-azidophenyl)imidazo[1,2-a][1,8]naphthyridine (17) are also reported.     

1,2-fused pyrimidines. V. Synthesis of 1-alkyl or phenyl-2H-dipyrido-[1,2-a:2′,3′-d]pyrimidine-2,5(1H)-diones

The reaction of 2-[(N-acyl, N-alkyl or phenyl)amino]-4H-pyrido[1,2-a]pyrimidin-4-ones 8a-g with the N,N-dimethylformamide/phosphorus oxychloride Vilsmeier reagent 1 (95°, 90 minutes) afforded 1-alkyl or phenyl-2H-dipyrido[1,2-a:2′,3′-d]pyrimidine-2,5(1H)^?diones, 3-alkyl substituted or not, 10a-g . The starting compounds 8 were prepared by treating 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones N-alkyl substituted 7a,b or N-phenyl substituted 4 with excess anhydrides (130°, 7 hours) when the 2-(alkylamino) derivatives 7 were used in the reaction, compounds 8 were obtained along with very small amounts of 3-acyl-2-(alkylamino)-4H-pyrido[1,2-a]pyrimidin-4-ones 9 .     

Condensation of 1-Substituted 1,2,3,9a-Tetrahydro-9H-imidazo[1,2-a]indol-2-one Derivatives with Aromatic Aldehydes

Condensation of 1-alkyl-, 1-allyl-, and 1-benzyl-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones with benzaldehydes in acetic acid and subsequent treatment of the reaction mixture with potassium hydroxide afforded 1-substituted 9a-(2-phenylethenyl)-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-one derivatives. 1-Methyl- and 1-ethyl-9a-[2-(4-dimethylaminophenyl)ethenyl]-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones were synthesized by alkylation of 9a-[2-(4-dimethylaminophenyl)ethenyl]-1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-one with methyl- and ethyl iodides in DMF in the presence of a strong base.     

Transformations of the pyrido[1,2-a]pyrazine ring system into imidazo[1,2-a]pyridines,imidazo[1,2-a]pyrimidines and 2-oxa-6a, 10c-diazaaceanthrylenes

Transformations of methyl 3-dimethylamino-2-(1-methoxycarbonyl-4-oxo-4H-pyrido[1,2-a]pyrazin-3-yl)acrylate with some cyanomethylenecarbonyl group containing compounds or cyanamide into imidazo-[1,2-a]pyridines, irmdazo[1,2-a]pyrimidines and 2-oxa-6a, 10c-diazaaceanthrylenes are described.     

Fused polycyclic nitrogen-containing heterocycles 20. Thiazolo[3,4-<Emphasis Type="Italic">a</Emphasis>]quinoxalines from 4-hydroxy-2-phenyliminothiazolidines and C-substituted 1,2-phenylenediamines

The condensation of 4-hydroxy-3,5-diphenyl-2-phenyliminothiazolidine with 4,5-dimethyl-1,2-phenylenediamine affords 7,8-dimethyl-3-phenyl-1-phenyliminothiazolo[3,4-a]quinox-alin-4(5 H)- one; the condensation with 1,2-phenylenediamines containing different substituents at positions 4 and 5 gives both theoretically possible isomeric thiazolo[3,4-a]quinoxalines, which differ in the distribution of these substituents between positions 7 and 8 in the benzene ring of the quinoxaline system. 3a-Hydroxy-7,8-dimethyl-3-phenyl-l-phenylimino-3,3a-di-hydrothiazolo[3,4-a]quinoxalin4(5 H)- one was isolated and characterized as the intermediate of the reaction giving rise to thiazolo[3,4-a]quinoxaline from 4,5-dimethyl-1,2-phenylene-diamine. This intermediate is a covalent hydrate of the final product.     

Synthesis of 1H-imidazo[1,2-a]imidazole

The synthesis and structure analysis of the unknown 1H-imidazo[1,2-a]imidazole ( 1 ) is described. The preparation involves alkylation of 2-aminoimidazole with bromoacetaldehyde diethyl acetal and subsequent hydrolysis and cyclization with hydrochloric acid. The structure was characterized by mass spectrometry and by ¹H-, ¹⁵N- and ¹³C-nmr of 1 and by ¹H-nmr of its 1-benzyl derivative 8 . An independent synthesis of 8 was accomplished via cyclization of 2-(N-dichloroethyl-N-benzyl)aminoimidazole ( 11 ).     

Quino[1,2-c]quinazolines. I. Synthesis of quino[1,2-c]quinazolinium derivatives and the related indazolo[2,3-a]quinoline derivatives as analogs of the antitumor benzo[c]phenanthridine alkaloids

9,10-Dimethoxy-1,2,3,4,12,13-hexahydro-1-oxoquino[1,2-c]quinazolinium perchlorate, 1,2,3,4,13,24-hexahydro-1-oxo[1,3]dioxolo[4,5-g]quino[1,2-c]quinazolinium perchlorate, 6-methyl-2,3,9,10-tetramethoxyquino-[1,2-c]quinazolinium perchlorate and 2,3-dimethoxy-13-methyl[1,3]dioxolo[4′,5′:6,7]quino[1,2-c]quinazolinium perchlorate were synthesized as analogs of the potent antitumor benzo[c]phenanthridine alkaloids nitidine and fagaronine. The related 2,3,8,9-tetramethoxyindazolo[2,3-a]quinoline and 2,3-dimethoxy[1,3]dioxolo-[4,5-g]indazolo[2,3-a]quinoline were also synthesized. Further, the novel formation of 6,7-dimethoxy-2-(2-ethylamino-4,5-dimethoxyphenyl)quinoline via reductive alkylation with Raney nickel in refluxing ethanol is also reported.     

The reduction and hydrolysis of some 7,7-diethylpyrazolo[1,2-a]-pyridazine-6,8(7H)dione derivatives

The chemistry of several of the Diels-Alder adducts formed by the reaction of 4,4-diethylpyrazoline-3,5-dione ( 1 ) with conjugated dienes was studied with respect to reduction (hydride and catalytic) and reaction with base. Reaction of the 2,3-dimethyl-1,3-butadiene adduct with lithium aluminum hydride followed by hydrogenation gave 1,3,5,6,7,8-hexahydro-cis-endo-6,7-dimethyl-2,2-diethylpyrazolo[1,2-a]pyridazine ( 11 ). Attempted conversion of this compound to 3,3-diethyl-cis-7,8-dimethyl-1,5-diazacyclononane ( 12 ) gave instead a compound which has been tentatively identified as N-(2,3-dimethyl-4-aminobutyl)-2-ethyl-2-methylbutanaldimine ( 14 ). Lithium aluminum hydride reduction of 4,4-diethylpyrazolidine-3,5-dione ( 22 ) or the adducts formed from 1 and cyclopentadiene or 1,3-cyclohexadiene gave good yields of 4,4-diethylpyrazolidine ( 21 ). This later reduction gave a new and efficient synthetic route to the pyrazolidine ring system. Lithium aluminum hydride reduction of 5,6,7,8-tetrahydro-5,8-ethano-2,2-diethylpyrazolo[1,2-a]pyridazine-1,3(2H)dione ( 26 ) followed by hydrogenolysis led to a high yield of 4,4-diethyl-2,6-diazabicyclo[5.2.2]undecane ( 28 ) which is the first reported example of this ring system. Reaction of several of the adducts with ethanolic potassium hydroxide resulted in the opening of the five-membered ring.     

3-Methylpyrazolo [1,2-a] pyridazin-1-one. Selenium derivatives of 5,8-dihydropyrazolo[1,2-a]pyridazine

The dehydrogenation of the known 3-methyl-5,8-dihydropyrazolo[1,2-a]pyridazin-1-one (2) to the ten π electron heteroaromatic 3-methylpyrazolo[1,2-a]pyridazin-1-one ( 3 ) is reported. Conversions of the pyrazolone 2 to the pyrazoloselenone 6 via the chloropyrazolium chloride 7 , and of pyrazolones 2 and 3 and pyrazoloselenone 6 into the corresponding O or Se ethyl pyrazolium fluoroborates 5, 4 , and 8 by triethyloxonium fluoroborate are also described.     

1,2-Fused pyrimidines. III. Derivatives of 12H-pyrido[1′,2′:1,2]pyrimido[4,5-b]quinoline,a novel heterocyclic system

Reactivities of 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones and 4-amino-2H-pyrido[1,2-a]pyrimidin-2-ones, both N,N-dialkyl and (N-alkyl, N-phenyl)substituted, when treated with the N,N-dimethylformamide/phosphorus oxychloride Vilsmeier-Haack reagent XII were compared. Starting from 2-[(N-alkyl, N-phenyl)amino] compounds IXa,b , the expected XVIa,b and XVIIa,b were obtained, which are derivatives of 12H-pyrido[1′,2′:1,2]pyrimido[4,5-b]quinoline, a novel heterocyclic system. When 2-(phenylamino) compound IXc was used a mixture of 3-formylderivative XVIII and 12H-pyrido-[1′,2′:1,2]pyrimido[4,5-b]quinolin-12-one ( XIX ) resulted from the reaction. On the other hand, 2-(dialkylamino)-4H-pyrido[1,2-a]pyrimidin-4-ones IIIa-c plainly afforded high yields of 3-formylderivatives XIVa-c. In contrast, no significant reaction occurred when 4-(dialkylamino) and 4-[(N-alkyl,N-phenyl)amino] compounds IIa-c and VIIIa,b were treated with the reagent XII , under the same as well as more severe conditions. A clear difference in the nucleophilic reactivity of C-3 position between these two classes of isomers is pointed out by the above summarized results.     

[1,3,5]Triazino[1,2-a] azepines: A new ring system

The reaction of 2-pyrrolidino-1-aza-1-cycloheptene with aryl isocyanates leads, via 1,4-dipolar cycloaddition, to 1,3-diaryl-10a-pyrrolidinoperhydro[1,3,5]triazino[1,2-a]azepine-2,4-diones. The reaction provides a facile route to the novel [1,3,5]triazino[1,2-a]azepine ring system.     

Formylation of 3,4-Dihydropyrrolo[1,2-a]pyrazines

Formylation of 3,4-dihydropyrrolo[1,2-a]pyrazines containing alkyl or aryl substituents at position 1 has been studied under the conditions of the Vilsmeier reaction. The direction of the reaction depends on the structure of 3,4-dihydropyrrolo[1,2-a]pyrazine starting materials. Formylation of 1-methyl-substituted 3,4-dihydropyrrolo[1,2-a]pyrazines occurs at the methyl group.