Short diastereoselective synthesis of cis- and trans-hexahydropyrido[2,1-a]isoindole derivatives

A new and highly stereoselective access to 4,10b-trans or 4,10b-cis hexahydropyrido[2,1-a]isoindole derivatives is reported, both requiring an intramolecular Mannich-type reaction as key step. The cis diastereoisomer is obtained in three steps from a 2-alkyl benzaldehyde through the stereoselective formation of a 2,6-cis-disubstituted piperidine, while the trans stereomer is efficiently obtained, in a single step, if a 2-formyl benzoic acid is involved in the Mannich cyclization process.     

On the reactivity of isoindolo[2,1-a]quinazoline-5-ones

Base- and acid-catalyzed nucleophilic addition of 11H-isoindolo[2,1-a]quinazoline-5-one to aromatic aldehydes and maleimides was investigated. The aldol adducts and condensation products were obtained stereoselectively. Main diastereomers of the Michael adducts were isolated in 74-89% yield, and converted by N-methylation to new stable α-substituted isoindole derivatives, for which 6-methylisoindolo[2,1-a]]quinazoline-5-one stands as the unsubstituted reference. The stability of the latter was monitored in moist aerated CDCl₃ solution, and one of the oxidative hydrolysis product was characterized by X-ray diffraction analysis as the corresponding N-arylphthalimide. The reactivity of the unsubstituted 6-methylisoindolo[2,1-a]]quinazoline-5-one was also investigated with acetylenic Michael acceptors. Fully conjugated isoindole derivatives possessing an original pull-push-pull structure were obtained. The conformations and molecular orbitals of the dibenzoylacetylene adduct were studied at the DFT level of theory. Its static quadratic hyperpolarizabilty β₀ was also calculated at the ZINDO level.     

Condensation of the isoindole–isoindoline isomers of the thieno[3′,2′:5,6]pyrimido[2,1-a]isoindol-6(10H)-one with aldehydes

The reaction of the isoindole–isoindoline isomers of the thieno[3′,2′:5,6]pyrimido[2,1-a]isoindol-6(10H)-one with aldehydes gives new benzylidene thieno[3′,2′:5,6]pyrimido[2,1-a]isoindol-6(10H)-one derivatives. The structures were assessed with NMR, UV spectroscopy and mass spectra.     

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 .     

Synthesis of the 5H-pyrrolo[2,1-a]isoindole ring with 1,3-dipolar cycloaddition reactions

The 1,3-dipolar cycloaddition reaction between mesoionic oxazolines, formed from either 1,3-dihydro-2-substituted-2H-isoindole-1-carboxylic acids or 1,3-dihydro-1-oxo-α-substituted-2H-isoindole-2-acetic acids, and dimethylacetylene dicarboxylate has led to the synthesis of several 5H-pyrrolo[2,1-a]isoindole derivatives 9a-d .     

Synthesis of novel imidazo[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines and pyrimido[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines

Several 1 1-amino-5H-pyrrolo[2,1-c][1,4]benzodiazepines have been used as starting material to prepare a number of derivatives of 9H-imidazo[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines and 10H-pyrimido[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepines. The imidazole nucleus was built by reaction of amidines with ethyl bromopyruvate or aminoacetaldehyde dimethylacetal. Several derivatives of imidazo[1,2-a]pyrrolo[2,1-c][1,4]benzodiazepine have been prepared by formylation of the pyrrole ring followed by formation of thioamides. Condensation of 11-amino-5H-pyrrolo[2,1-c][1,4]benzodiazepines with diethyl ethoxymethylenemalonate afforded intermediate diesters which were transformed into the corresponding 10H-pyrimido[1,2-a]pyrrolo[2,1-c]-benzodiazepines.     

Microwave assisted synthesis of novel imidazo [2,1-b]thiazole derivative attached to quinoxalinones

3-(6-Phenylimidazo[2,1-b]thiazol-5-yl)quinoxalin-2(1H)-ones (qunoxalinone) (6a-q) have been synthesized by the reaction of ethyl 2-oxo-2-(6-phenylimidazo[2,1-b]thiazol-5-yl)acetates (4a-e) with suitably substituted o-phenylenediamines (5a-f) under microwave heating. The ethyl 2-oxo-2-(6-phenylimidazo[2,1-b]thiazol-5-yl)acetates (4a-e) were prepared by the reaction of 6-phenylimidazo[2,1-b]thiazoles (3a-e) with ethyl chlorooxoacetate in refluxing 1,4-dioxane whereas the thiazoles (3a-e) were synthesized by the reaction of 2-bromo-1-phenylethanones (2a-e) with thiazol-2-amine in refluxing acetone.     

Photochemistry of stilbenyl-pyrroles: a new approach to indole and isoindole derivatives

A new 2-{2-[2-(4-methylphenyl)ethenyl]phenyl}pyrrole (11) was prepared and transformed by a photochemical reaction furnishing two cyclised products 4,5-dihydro-4-(p-methylphenyl)benzo[g]indole (12) and 4H-4-(p-methylbenzyl)pyrrolo[2,1-a]isoindole (13), and a reduction product, 2-{2-[2-(4-methylphenyl)ethyl]phenyl}pyrrole (14).     

Contributions to syntheses of pyrrolo[2,1-a]phthalazines

Abstract  

Structural elucidation of the dihydro derivatives obtained as by-products in the classic salt method synthesis of pyrrolo[2,1-a]phthalazines and acetylenic dipolarophiles was achieved by X-ray diffraction analysis of a representative compound. In addition, new pyrrolo[2,1-a]phthalazines were obtained by a one-pot three-component reaction that avoids the formation of the dihydro derivative intermediates.     

Multicomponent Transformation of Isoindoline‐1,3‐diimine (=1H‐Isoindole‐1,3(2H)‐diimine), Acetylenic Esters,and Triphenylphosphine to Novel Dihydropyrimido[2,1‐a]isoindole Derivatives

The three‐component reaction of the zwitterions generated from dialkyl acetylenedicarboxylates (=dialkyl but‐2‐ynedioates and triphenylphosphine (Ph₃P) with isoindoline‐1,3‐diimine (=1H‐isoindole‐1,3(2H)‐diimine) is described (Scheme 1). This reaction affords the corresponding special type of substituted dihydropyrimido[2,1‐a]isoindole derivatives in good yields without using any catalyst and activation (Table).     

Synthesis of novel tricyclic isoindole derivatives

Novel 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindoles were prepared from the thermolysis of (3R,9bS)-5-oxo-2,3,5,9b-tetrahydrothiazolo[2,3-a]isoindole-3-carboxylic acids in acetic anhydride. The structure of 3-methylene-2,5-dioxo-3H,9bH-oxazolo[2,3-a]isoindole 6a was determined by X-ray crystallography.     

Ring closure reactions with nitriles. I. Formation of pyrrolo [2,1-c] [1,2,4] benzothiadiazines and pyrrolo[1,2-a] quinazolines

Pyrrolo[2,1-c][1,2,4]benzothiadiazines have been prepared from the reactions of o-amino-benzenesulfonamides with γ-cyanopropionaldehydes. Pyrrolo[1,2-a]quinazolines have been prepared from the reaction of anthranilamides with either γ-cyanopropionaldehyde or succinic anhydride. The cyclization of a 4-oxo-2-quinazolinepropionic acid has produced a pyrrolo-[1,2-a]quinazoline and the isomeric pyrrolo[2,1-b]quinazoline.     

Design,synthesis, and biological evaluation of novel substituted imidazo[2,1-a]isoindole derivatives as antibacterial agents

An efficient protocol has been developed for the synthesis of fused imidazo[2,1-a]isoindol-5-ones (2a–d) from 2-iodo benzoic acids and N,N-carbonyldiimidazole (CDI) using one-pot Pd-catalyzed C?C bond coupling. The reaction of imidazo[2,1-a]isoindol-5-one (2a–d) with substituted α-bromo ketones in toluene afforded corresponding imidazo[2,1-a]isoindolium derivatives (3a–i) in good yields. The structures of the title compounds were well established on the basis of infrared (IR), ¹H NMR, carbon-13 nuclear magnetic resonance (¹³C NMR), mass spectral data, and elemental analysis (C, H, and N). In vitro antibacterial results revealed that, the compounds 3b and 3i were found to possess an excellent broad spectrum of inhibiting potency against all the tested bacterial strains with minimum inhibitory concentration values ranging from 3.125 to 25?µg mL^?1.     

Photocatalytic Oxidative [3+2] Cycloaddition for Pyrrolo[2,1-a]isoquinoline Synthesis Using a Porphyrin-Based Covalent Organic Framework

By using a catalytic amount of a porphyrin-based covalent organic framework (Por-Ad-COF) as the efficient recyclable photocatalyst, the photocatalytic oxidative [3+2] cycloaddition reaction between tetrahydroisoquinolines and N-substituted maleimides was developed under aerobic conditions at room temperature. Various substituted pyrrolo[2,1-a]isoquinolines were obtained in moderate to good yields via the dipolar [3+2] cycloaddition and oxidative aromatization cascade process under visible light irradiation. This was the first example to employ the covalent organic framework as the heterogeneous photocatalyst to perform the photocatalytic dipolar [3+2] cycloaddition reaction for the synthesis of pyrrolo[2,1-a]isoquinolines.     

New heterocyclic structures. [1,3]Thiazino[3,2-a]purine and [1,2,3]triazolo[4,5-d][1,3]thiazino[3,2-a]pyrimidine

Derivatives of two new molecular structures, namely, [1,3]thiazino[3,2-a]purine and [1,2,3]triazolo[4,5-d]-[1,3]thiazino[3,2-a]pyrimidine, were synthesized together with other heterocyclic compounds. Retrosynthetic analysis of their molecular skeletons suggested a simple way of obtaining 3,4-dihydro-7,8-diamino-2H,6H-pyrimido[2,1-b][1,3]thiazin-6-one, which is a useful intermediate for their synthesis. This intermediate and the thiazole homologue were obtained directly by reaction of 5,6-diamino-2,3-dihydro-2-thioxo-4(lH)-pyrimidi-none with 1,3- or 1,2-dibromoalkane, respectively.     

Zinc triflate-catalyzed synthesis of pyrazino[2,1-b]quinazoline-3,6-diones

Using zinc triflate, the direct one-pot double cyclodehydration of linear tripeptides to the total synthesis of pyrazino[2,1-b]quinazoline-3,6-diones (1a-l) on solid support was achieved with good overall yields in short reaction time. These syntheses of the pyrazino[2,1-b]quinazoline-3,6-diones were conveniently achieved in only three steps, starting from the amino acid-bound Wang resin.     

Synthesis of imidazo[4,5-a]acridones and imidazo[4,5-a]acridines as potential antibacterial agents

Abstract  

New imidazo[4,5-a]acridone derivatives were synthesized from the rearrangement of 3H-imidazo[4′,5′:3,4]benzo[c]isoxazoles. New imidazo[4,5-a]acridines were obtained from the reaction of imidazo[4,5-a]acridones in boiling POCl₃. All of these compounds exhibited antimicrobial activities comparable to streptomycin as reference drug.     

A new approach towards the synthesis of pyrrolo[2,1-a]isoquinolines

Reaction of 5-bromo-2-methyl-8-nitro-1,2,3,4-tetrahydroisoquinoline with activated alkynes affords stable tetrahydropyrrolo[2,1-a]isoquinolin-4-ium ylides. Further reactions of ylide 2 gives access to substituted dihydropyrrolo[2,1-a]isoquinolines in good yields.     

A facile one-pot synthesis of 6,7,8,9-tetrahydrobenzo[4,5]thieno[2,3-d]-1,2,4-triazolo[4,5-a]pyrimidin-5-ones

Abstract  

The reaction of 2-mercapto-6,7,8,9-tetrahydro-3H-benzo[4,5]thieno[2,3-d]pyrimidin-4-one or its 2-methylthio derivative with hydrazonoyl halides, in the presence of triethylamine, yielded 6,7,8,9-tetrahydrobenzo[4,5]thieno[2,3-d]-1,2,4-triazolo[4,5-a]pyrimidin-5-ones. The structure of the latter compounds was further confirmed by reaction of 2-mercapto-6,7,8,9-tetrahydro-3H-benzo[4,5]thieno[2,3-d]pyrimidin-4-one with the appropriate active chloromethylenes followed by coupling of the products with benzenediazonium chloride to afford the non-isolable azo-coupling products which converted, in situ, to 6,7,8,9-tetrahydrobenzo[4,5]thieno[2,3-d]-1,2,4-triazolo[4,5-a]pyrimidin-5-ones. The reaction mechanism was proposed and the products were screened for their biological activity. Some of the newly synthesized compounds had a moderate effect against some bacterial and fungal species.     

Synthesis and rearrangement of cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones: an access to cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones

2-Substituted-4a-hydroxy-9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 2a-c were synthesized by an one-step cyclocondensation from the 5-substituted-2-amino-2-oxazolines 1a-c with ethyl 2-oxocyclohexanecarboxylate in ethanol at room temperature, and easily dehydrated to provide 2-substituted-9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-9-ones 3. In refluxing xylene, the reaction conducted with various ethyl 2-oxocycloalkanecarboxylates led to the two isomeric 2-substituted-8/9H-cycloalkyl[1,2-e]oxazolo[3,2-a]pyrimidin-8/9-ones 3 and 2-substituted-5H-cycloalkyl[1,2-d]oxazolo[3,2-a]pyrimidin-5-ones 4. The structure of some compounds was unambiguously established using X-ray crystallography. According to results from the DSC analysis of compound 2a, formation of the thermodynamically stable pyrimidinones 4 could be related to an intramolecular rearrangement of kinetically controlled pyrimidinones 3.