1-(2-pyridyl)-3,4-dihydro-6,7-dimethoxyisoquinoline and some of its hydrogenated and N-substituted derivatives

The preparation of 1-(2-pyridyl)- and 1-(2-piperidyl)-substituted, partly hydrogenated derivatives of 6,7-dimethoxyisoquinoline is described.     

Novel reactions of 6,7-dimethoxy-3,4-dihydroisoquinoline and 3,4-dihydro-β-carboline with dipolarophiles

New reactions of 6,7-dimethoxy-3,4-dihydroisoquinoline and 3,4-dihydro-β-carboline with various electron-deficient olefins are described. ‘One-pot’ generation and cycloaddition of the 1,3- and 1,4-dipoles formed from these heterocycles with a range of alkene dipolarophiles affords cycloadducts in good yields with high regio- and stereoselectivity.     

Fragmentation of enamides derived from 6,7-dimethoxy-4-methyl-2H-1,3-benzothiazin and 3,4-dihydro-6,7-dimethoxy-1-methylixopuinoline

The electron impact mass spectra of several enamides have been examined. The enamides were prepared by reaction of aroyl halides with 6,7-dimethoxy-4-methyl-1,3-benzothiazin, and with 3,4-dihydro-6,7-dimethoxy-l-methylisoquinoline. The fragmentation pathways that have been proposed are supported by ion composition determinations and by mass-analysed ion kinetic energy spectrometry experiments carried out on the molecular ions and major fragment ions. The spectra are characterized by a loss of carbon monoxide from the molecular ion of each compound, a process which is accompanied by migration of the aryl group.     

Synthesis of 6,7-methylenedioxy-3,4-dihydro-1-methylbenzothieno[2,3-c]pyridine

Synthesis of the title compound, a potential inhibitor of mouse brain monoamine oxidase, is described. The preparation proceeds in eight steps from 1,3-benzodioxole in 1.9% overall yield. The novel hydrogenolysis of an aryl thiocyanate to the aryl methyl sulfide is reported.     

Site-selective photocycloadditions of 2-pyrones with electron-poor olefins and the derivation from the cycloadducts

Photosensitized cycloaddition of 4,6-dimethyl-2-pyrone ( 1 ) with methacrylonitrile ( 3b ) afforded two types of [2 + 2]cycloadducts, 4b and 6b , across the C₅-C₆ and C₃-C₄ double bonds in 1 , respectively. Photosensitized reactions of 1 with dimethyl maleate and dimethyl cyclobutene-1,2-dicarboxylate gave [2 + 2]cycload-ducts 4d, 4e across the C₅-C₆ double bond, in addition to [4 + 2]cycloadduct 9d or bicyclo[4.2.0]octadiene 10e . The photoreactions of methyl 2-pyrone-5-carboxylate ( 2 ) with 3b and 2-chloroacrylonitrile ( 3c ) gave [4 + 2]cycloadducts 5b, 5c in addition to [2 + 2]cycloadducts 11b and 11c across the C₅-C₆ double bond in 2 . The photocycloaddition mechanism was explained from results calculated by means of PM3-CI method. Namely, the site- and/or regio-selective products, 4, 5, 8, 9 and 10 were thought to come from the same site-selective radical intermediates in the case of electron-poor olefins. Pyrolysis and/or hydrolysis of the cycload-ducts 4e, 5b, 5c gave 5,6-dihydro-2-pyrone 12 or benzene derivatives.     

Synthesis of 6,7-Dihydroindazole and 7,8-Dihydroquinazoline Derivatives from Ethyl 4,4-Dimethyl-9-oxo-3,4-dihydro-9H-xanthene-2-carboxylates

Russian Journal of General Chemistry - A procedure has been developed for the synthesis of 6,7-dihydroindazoles and 7,8-dihydroquinazolines by reaction of 3,4-dihydroxanthone derivatives with 1,2-...     

Synthesis of some 3-alkenyl-4-oxo-6,7-dihydro-4H-pyrano[3,4-d]isoxazoles

A series of 3-alkenyl-4-oxo-6,7-dihydro-4H-pyrano[3,4-d]isoxazole derivatives was prepared by reaction of hydroxylamine with 4,5-dioxo-2,3,7,8-tetrahydro-4H,5H-pyrano[4,3-b]pyran derivatives.     

Stereospecific synthesis of 6,7-dihydro-5H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines

The reaction of 3-mercapto-4-arylideneamino-1,2,4-triazoles 2b-d , 3a-d with ethyl bromoacetate and/or phenacyl bromide in hot DMF and triethylamine affords the stereochemically pure 7-acyl-6-aryl-6,7-dihydro-5H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazines 4b-d , 5a-d , 6b , d in which the consecutive hydrogen atoms N(5)H-C(6)H-C(7)H are cis to each other. This stereochemistry was determined by ¹H NMR spectroscopy and confirmed by comparison with the spectrum of 3,6-diphenyl-6,7-dihydro-5H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazine 10 . The latter was prepared by NaBH₄ reduction of 3,6-diphenyl-5H-1,2,4-triazolo[3,4-b][1,3,4]thiadiazine 9 . The reported reactions offer two interesting stereospecific syntheses of the condensed heterocyclic compounds.     

Stereochemistry of the synthesis of 1,2,3,4-tetrahydrocinnolines from aryldiazenium salts and olefins

It follows from the PMR spectra that the reaction of 1-methyl-, 1-phenyl-, 1-ethyl-,1-phenyl-, and 1,1-diphenyldiazenium salts with cis- and trans-d-styrenes, which leads to the corresponding 3-d-4-phenyl-1,2,3,4-tetrahydrocinnolines, takes place with retention of the configuration in the starting styrenes. It is therefore proposed that this reaction be regarded as a special case of [4⁺_s + 2_s]-cycloaddition.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1658–1661, December, 1977.     

New synthesis of 1-[(3,4-dimethoxyphenyl)methoxymethyl]-6,7-dimethoxyisoquinoline (setigerine), a naturally occurring alkaloid, and some derivatives of papaverine

A novel and improved synthetic route for the preparation of the new alkaloid setigerine, isolated from Papaver setigerum DC, and some new 3,4-dihydropapaverine and papaverine derivatives is reported. This method is based on the side chain chlorination of 1-benzyl-3,4-dihydroisoquinolines using N-chlorosuccinimide (NCS) and subsequent reaction with sodium methoxide in methanol to give the corresponding isoquinolines.     

Formation of 3,4-dihydro-α-carbolines from 2-aminoindole

In the condensation of 2-aminoindole with ,-unsaturated oxo compounds, in contrast to ordinary aromatic amines and a number of heterocyclic amines, the direction of cyclization is reversed. The general scheme of the reaction includes the reaction of the position of 2-aminoindole with the activated double bond of the oxo compound via a mechanism of the Michael type and condensation of the carbonyl group of the unsaturated carboline structure, which subsequently undergoes aromatization. The intermediate 3,4-dihydro--carbolines were produced and isolated; this made it possible in a number of cases to establish the structures of the final -carbolines. The structures of the 3,4-dihydro compounds were confirmed by the set of spectral characteristics. Data from the UV, IR, PMR, and mass spectra are presented.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 945–951, pp. 945–951, July, 1977.     

The reaction of benzotriazoles with 3,4-dihydro-4H-pyrane and 2-acetoxymethyl-3,4-dihydro-2H-pyrane

From the reaction of benzotriazoles with 2,3-dihydro-4H-pyrane and 2-acetoxymethyl-3,4-dihydro-2H-pyrane the corresponding 1-(2-tetrahydropyranyl)benzotriazole and cis-and trans-1-(6-acetoxymethyl-2-tetrahydropyranyl)benzotriazole derivatives were obtained. The structures and conformations of these compounds were confirmed by UV and NMR spectra.     

Synthesis and Stereochemistry of flavan-3,4-diol diacetates

Two hitherto unknown racemates of flavan-3,4-diol diacetate have been prepared and NMR data now available for the complete set of four racemates establish the stereochemistry of these compounds.     

Synthesis of 3-benzoyl-3,4-dihydro-2H- and 3,4-dihydro-2,2-disubstituted-benzopyrans via alkynyl grignard reagents

The versatility of the new route to a substituted chromane via a lithiated allene recently described by us [1] is reported. The relatively more stable alkynols 2–4 were readily identified and thus provide evidence for the formation of vinyl acetylene carbinol as an intermediate in the new route. Accordingly, phenylacetylene magnesium bromide [2] reacted with suitable aldehyde or ketone to give the alkynols 2–4 which condensed further with the same or different aldehyde or ketone to give 3-benzoyl heteroring-substituted chromanes 5–17.     

Chemoselective O-tert-butoxycarbonylation of phenols using 6,7-dimethoxyisoquinoline as a novel organocatalyst

The chemoselective O-tert-butoxycarbonylation of phenols using low levels (5-0.1 mol %) of 6,7-dimethoxyisoquinoline as a reusable organocatalyst is described.     

Photocyclization of 1-(2-halophenyl)-3,4-dihydro-6,7-dimethoxyisoquinolines: a short and new synthesis of triclisine

A short and new synthesis of the non-phenolic azafluoranthene alkaloid triclisine utilizing the photocyclization of 1-(2-halophenyl)-3,4-dihydro-6,7-dimethoxyisoquinolines as a key step has been described.     

Synthesis and opening of the thiadiazine ring in 6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines

A reaction of 3-benzylthiotriazole-4-amines with aromatic aldehydes leads to the formation of 6,7-dihydro-5H-[1,2,4]triazolo[3,4-b][1,3,4]thiadiazines. A dihydrothiadiazine ring opening along the N-N bond occurs by the action of strong bases. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1249–1252, June, 2008.