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 method for the synthesis of pyrrolo[1,2-a]pyrazines and pyrrolo[1,2-a] quinoxalines

A new method is proposed for the synthesis of pyrrolo[1,2-a]pyrazines and pyrrolo[1,2-a]-quinoxalines. By the alkylation of sodium derivatives of 2-acylpyrroles with -bromo carbonyl compounds or their acetals and subsequent treatment of the reaction products with ammonium acetate in acetic acid, a number of derivatives of pyrrolo[1,2-a]pyrazine, including the first member of the class, pyrrolo[1,2-a]pyrazine itself, have been obtained. Similarly, from 2-benzoylpyrrole and the dimethyl ketal of -bromocyclohexanone was obtained 4-phenyltetrahydropyrrolo[1,2-a]quinoxaline, which readily dehydrogenates in the presence of Raney nickel to form 4-phenylpyrrolo[1,2-a]quinoxaline.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 8, pp.1048–1050, August, 1970.     

One-pot synthesis of pyrrolo[1,2-a]quinoxalines

A transition metal-free process for the regioselective synthesis of pyrrolo[1,2-a]quinoxalines under mild conditions in one-pot is described. The reaction afforded a variety of products in good to excellent yields. Indolo[1,2-a]quinoxalines were also synthesized from indole-2-carboxamides under the same conditions.     

Synthesis of pyrrolo[1,2-a]indoles from 2-arylidene-3-indolinones

Chemistry of Heterocyclic Compounds -     

Catalytic asymmetric dipolar cycloadditions of indolyl delocalized metal-allyl species for the enantioselective synthesis of cyclopenta[b]indoles and pyrrolo[1,2-a]indoles

The development of novel synthons and efficient methods to synthesize chiral polycyclic indoles has been a hot topic in organic synthesis and medicinal chemistry owing to their broad applications in medicines, pesticides, and other functional molecules.Here, we disclosed novel indolyl substituted metal-allyl zwitterionic intermediates through the decarboxylation of conveniently available vinyl indoloxazolidones, which could be regarded as two types of dipolar species through the anionic delocalization.The palladium-π-allyl species tended to serve as an all-carbon 1,3-dipole in the asymmetric [3+2] cycloaddition with electrondeficient alkenes, which furnished polysubstituted cyclopenta[b]indoles with high regio-and stereoselectivities. Meanwhile, the iridium-π-allyl species was recognized as an aza-1,3-dipole in asymmetric [3+2] cycloaddition with in situ generated C1 ammonium enolates, affording pyrrolo[1,2-a]indoles with high diastereo-and enantioselectivities. In addition, the dipolar cycloadditions could be easily scaled-up and several synthetic transformations of the cycloadducts were demonstrated for the rapid synthesis of diverse chiral polycyclic indoles.     

Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles

N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6-tetrahydropyrazines.     

An efficient synthesis of 9H-pyrrolo[1,2-a]indoles

A novel and effective method has been developed for the synthesis of 9H-pyrrolo[1,2-a]indoles by treatment of 3-substituted-4,6-dimethoxyindoles with chalcones in the presence of hydrochloric acid.     

Acylation of pyrrolo[1,2-a]pyrazines

The acylation of pyrrolo[1,2-a]pyrazines with acetic anhydride and the acid chlorides of various carboxylic acids has been studied. It has been shown that pyrrole[1,2-a]pyrazines are selectively acylated at the α-position of the pyrrole ring when it is free. Products of the condensation of 1-methylsubstituted pyrrolo[1,2-a]pyrazines have been obtained for the first time in the process of acetylation. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, 263–272, February, 2008.     

Synthese de pyrrolo[1,2-a]quinoleines

A-Acetoxypyrrolo[1,2a]quinolines 26-30 were synthesized by cyclization of 2-(1-pyrroly)phenylacetic acids 21-25 with acetic anhydride. The structures of the new compounds were determined by ¹H-nmr spectroscopy.     

Asymmetric synthesis of pyrrolo[1,2-a]indoles via organocatalytic[3 + 2] annulation of substituted 2-vinylindoles with azlactones

The chiral phosphoric acid catalyzed asymmetric[3+2]annulation of substituted 2-vinylindoles with azlactones has been established.This reaction represented a practical approach for the synthesis of structurally diverse pyrrolo[1,2-a]indoles with two vicinal stereocenters including one tetrasubstituted stereocenter in good yields and good stereoselectivities under mild conditions.     

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.     

Protonation of pyrrolo[1,2-a] imidazole derivatives

The protonation of a number of pyrrolo[1,2-a]imidazole derivatives in trifluoroacetic acid was studied by PMR spectroscopy. The 5,7-unsubstituted compounds form a mixture of two forms of cations, the structures of which correspond to the addition of a proton to the C₅ and C₇ atoms of the two-ring system with predominance (60–90%) of the 5-C cation. The introduction of a CH₃ group into the 5 position changes the direction of protonation to favor predominant (95%) formation of the 7-C cation. The 7-methyl derivatives of pyrroloimidazole are protonated exclusively at the C₅ atom. It is demonstrated that the basicity of the pyrroloimidazoles considerably surpasses the basicity of indolicine derivatives. The comparative proton-acceptor capacity of these systems is compared with the energy indexes and the reactivity indexes calculated by the simple MO LCAO method.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 492–497, April, 1972.     

Synthesis of pyrrolo[1,2-a]pyrimidine derivatives

8-Cyanopyrrolo[1,2-a]pyrimidines, the cyano group of which is eliminated when they are heated with phosphoric acid, were obtained by reaction of 2-amino-3-cyanopyrroles with acetylacetone.Compounds Ia, c-g were described earlier in [3], while Ib, h are described in the present work.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1677–1681, December, 1976.     

Protonation of pyrrolo[1,2-a]benzimidazole derivatives

The protonation of a number of pyrrolo[1,2-a]benzimidazole derivatives in trifluoroacetic acid was studied by PMR spectroscopy. 1,3-Unsubstituted compounds are protonated exclusively at the C₁ atom. Under similar conditions, pyrrolobenzimidazoles that have a methyl group in the 1 position form a mixture of two protonated forms, which correspond to the addition of a proton to C₁ and C₃, respectively. The relative percentage of the C₃-protonated form decreases successively (from 81 to 18%) on passing from the 3-unsubstituted compound to the corresponding 3-phenyl and 3-methyl derivatives. The basicity constants of the pyrrolobenzimidazoles decrease symbatically with an increase in the relative percentage of this form. The relative proton-acceptor capacity of indolicine, pyrrolo[1,2-a]-imidazole, and pyrrolo[1,2-a]benzimidazole were examined on the basis of the protonation data and the reactivity indexes, calculated by the simple Hückel MO method.Translated from Khimiya Geterotsiklicheskih Soedinenii, No. 8, pp. 1132–1137, August, 1972.