Tetrahydro- and octahydropyrido[1,2-a]pyrimidin-4-ones

The catalytic hydrogenation of 2-methyl-, 1 2,8-dimethyl-, 2 , 2,9-dimethyl-, 3 , 9-methyl-2-propyl-, 4 , 2,3,9-trimethyl-, 5 , 9-methyl-2-phenyl-, 6 , 9-hydroxy-2-methyl-, 7 , 9-acetoxy-2-methyl, 8 , 9-carboxy-2-methyl-, 16 , 9-carboethoxy-2-methyl-, 17 , 9-carbomethoxy-2-methyl-, 18 , and several 9-carboxamido-2-methyl-, 19, 20 , and 21 , derivatives of the pyrido[1,2-a]pyrimidin-4-one heterocycle has led to a series of novel 6,7,8,9-tetrahydro- and fully saturated, octahydro analogs. In deuteriochloroform or DMSO-d₆ solution, the pmr spectra of the tetrahydro derivatives derived from 1-7 revealed only the 6,7,8,9-tetrahydro structures. In the pmr spectra of 16-21 , there was evidence of a facile 1,3-prototropic shift of the proton from position-9 to position-1, resulting in equilibria between tautomeric species, i.e., . The ratio of tautomers present at equilibrium, with the esters, favored the enamine conformation, whereas, with both the carboxylic acid and the amides, the imine structure predominated. Supportive evidence for the enamine structure with the esters was derived also from the ir spectra. Alkylation of the anion derived from the tetrahydro 9-carbomethoxy derivative with sodium hydride led exclusively to derivatives of 6,7,8,9-tetrahydro system.     

Syntheses of optically active tetrahydro-1H-pyrrolo[1,2-a]imidazol-2-ones and hexahydroimidazo[1,2-a]pyridin-2(3H)-ones

The reactions of (2S)-2-amino-2-substituted-N-(4-nitrophenyl)acetamides 16a-c, succindialdehyde (13), and benzotriazole afforded enantiopure (3S,5R,7aR)-5-(1H-1,2,3-benzotriazol-1-yl)-3-substituted-1-(4-nitrophenyl)tetrahydro-1H-pyrrolo[1,2-a]imidazol-2-ones 17a-c, which were converted by sodium borohydride into (3S,7aR)-3-substituted-1-(4-nitrophenyl)tetrahydro-1H-pyrrolo[1,2-a]imidazol-2-ones 18a-c. Chiral (2S)-2-amino-2-substituted-N-(4-methylphenyl)acetamides 12a-d, easily prepared in two steps from N-Boc-alpha-amino acids 10a-d, similarly reacted with glutaraldehyde (20) and benzotriazole to generate 5-benzotriazolyl-3-substituted-hexahydroimidazo[1,2-a]pyridin-2(3H)-ones 21a-d, which were converted by sodium borohydride directly into optically active 3-substituted-hexahydroimidazo[1,2-a]pyridin-2(3H)-ones 22a-d.     

Electronic structure of 4H-pyrido[1,2-a]pyrimidin-4-ones

The characteristic features of ir and uv spectra of 43 4H-pyrido[1,2-a]pyrimidin-4-one derivatives with electron donor or acceptor groups in position 3, and positions 6, 7, 8, or 9, respectively, have been systematically studied. On the basis of the spectra some conclusions have been drawn for the molecular structure. The negative solvent effect of the lowest-energy π → π* transition is investigated by the PPP method.     

Synthesis of derivatives of pyrazino[1,2-a]pyrimidin-4-ones

3-Alkoxy-2-aminopyrazines have been condensed with ethyl ethoxymethylenemalonate and isopropylidene methoxymethylenemalonate to afford 9-alkoxypyrazino[1,2-a]pyrimidin-4-ones substituted in the first case by an ethoxycarbonyl group at 3 position.     

Synthetic approaches to hexahydropyrrolo[1,2-b]isoquinolones

Synthetic routes to 1,2,3,5,10,10a-hexahydropyrrolo[1,2,-b]isoquinolin-5-ones functionalized at C-10 were investigated. Attempts to prepare the ketone 2 , and subsequently introduce the desired C-10 hydroxymethylene group were unsuccessful due to the failure of 6 to cyclize and the unreactivity of 9 to relevant nucleophiles. Compound 1 was prepared by the condensation of 1-pyrroline with 7-methoxyisobenzopyran-1,3,-(4H)-dione to give 12 in quantitative yield. Acyl halide formation and subsequent reduction gave the desired compound 1.     

Alkylation of 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones

Reaction of 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones with dimethyl sulfate and haloalkanes in DMF or DMSO in the presence of potassium hydroxide gives the 1-substituted 1,2,3,9a-tetrahydro-9H-imidazo[1,2-a]indol-2-ones (N-substituted products) and 9,9a-dihydro-3H-imidazo[1,2-a]indoles (O-substituted products). The latter, on treatment with acids and bases, are converted into 1-alkoxycarbonylmethyl-2,3-dihydro-1H-indoles. 1-Ethoxycarbonyl-methyl-2,3-dihydro-1H-indoles on treatment with lithium aluminohydride undergoes cyclization to 2,3,9,9a-tetrahydrooxazolo[3,2-a]indole.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 1, pp. 49–53, January, 1988.     

A novel and convenient synthesis of thiazolo[3,2-a]pyrimidin-7-ones and pyrido[1,2-a]pyrimidin-2-ones using Vilsmeier reagent

A novel route for the synthesis of thiazolo[3,2-a]pyrimidin-7-ones and pyrido[1,2-a]pyrimidin-2-ones from acetylated 2aminothiazoles and 2-aminopyridines under Vilsmeier conditions has been developed.The plausible mechanism has also been proposed.     

Microwave-assisted combinatorial synthesis of polysubstituent imidazo[1,2-a]quinoline, pyrimido[1,2-a]quinoline and quinolino[1,2-a]quinazoline derivatives

A series of unusual fused heterocyclic compound derivatives, consisting of a pyridine and a imidazole or pyrimidine core, with a bridgehead nitrogen, were successfully synthesized by a microwave-assisted, three-component domino reaction of aldehydes, enaminones, and malononnitrile. In this one-pot reaction, up to five new bonds were formed accompanied by generating the lactam group. This method has the advantages of short synthetic route, operational simplicity, increased safety for small-scale high-speed synthesis, and minimal environment impact.     

Pyrimido[1,2-a]benzimidazolocyanines

Cyanine dyes containing a pyrimido[1,2-a]benzimidazole chromophore are described.     

Mass spectra of pyrrolo [1,2-a]benzimidazole and imidazo[1,2-a]benzimidazole derivatives

The closeness of the electronic structures of the ions formed in the first act of disintegration of the ions is responsible for the monotypic character of the subsequent fragmentation of pyrrolo[1,2-a]benzimidazole and imidazo[1,2-a]benzimidazole derivatives. The mass-spectrometric disintegration of the investigated systems has something in common with the fragmentation of thiazolo[3,2-a]benzimidazole derivatives.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, 1124–1127, August, 1975.     

Synthesis of 4-Aryl Benzimidazolo[1,2-a]-s-triazin-2-ones and 2-Aroylaminobenzimidazolo[1,2-b]-1,2,4-thiadiazolines

Reaction of 2-aminobenzimidazole with aroylisothiocyanates gave 2-aroylaminobenzimidazoles ( 3 ) and N-aroyl-N′-(benzimidazol-2-yl)-thioureas ( 4 ). The products obtained on reaction of 4 with PCl₅ in POCl₃, and with oxidising agents have been identified as 4-arylbenzimidazolo[1,2-a]-s-triazin-2-ones ( 5 ) and 2-aroylamino-benzimidazolo[1,2-b]-1,2,4-thiadiazolines ( 7 ) respectively.     

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.     

One-Pot Synthesis of [1,2]Isoxazolidin-5-ones and [1,2]Oxazin-6-ones

This article has been retracted.     

One-pot synthesis of imidazo[1,2-b]pyrazole,imidazo[1,2-b]-1,2,4-triazole,imidazo[1,2-a]pyridine,imidazo[1,2-a]pyrimidine,imidazo[1,2-a]benzimidazole,and 1,2,4-triazolo[4,3-a]benzimidazole derivatives

Hydrazonoyl bromides 1a-c react with 5-amino-3-phenyl-1H-pyrazole, 5-amino-1H-1,2,4-triazole, 2-aminopyridine, and 2-aminobenzimidazole to afford the corresponding imidazol[1,2-b]pyrazoles 10, imidazo[1,2-b]-1,2,4-triazoles 11, imidazo[1,2-a]pyridines 16, imidazo[1,2-a]pyrimidines 17, and imidazo[1,2-a]benzimidazoles 20, respectively. Compounds 1a-c reacted also with 2-methylthiobenzimidazole to give 1,2,4-triazolo[4,3-a]benzimidazole derivatives 21. © 1997 John Wiley & Sons, Inc.     

A convenient synthesis of 9H-dibenz[c,f]imidazo[1,2-a]azepin-9-ones

A convenient three step synthesis of 9H-dibenz[c,f]imidazo[1,2-a]azepin-9-ones from readily available 2-phenylimidazoline and a methyl benzoate is described.