Synthesis and absorption spectra of 2-substituted 5,8-dimethoxy-4H-1-benzothiopyran-4-one 1,1-dioxides

2,3-Dibromo-5,8-dimethoxy-4H-1-benzothiopyran-4-one (thiochromone) 1,1-dioxide which was a starting material to prepare sulfone analogues of 1,4-naphthoquinone dyes was easily prepared from 5,8-dimethoxythiochroman-4-one by oxidation and bromination. The reactions of 2,3-dibromo-5,8-dimethoxythiochromone 1,1-dioxide 4 with aliphatic and aromatic amines in ethanol below 20° gave 2-substituted derivatives 12a-e and at higher reaction temperature the amination gave 2-arylamino derivatives 13c-e debrominated at C -3. The visible absorption spectra of these derivatives were investigated by the PPP MO method.     

A simple, rapid and efficient protocol for the synthesis of methylthiomethyl esters under Swern oxidation conditions

A rapid, mild and high yielding method for the synthesis of methylthiomethyl esters is reported from the corresponding aliphatic, aromatic and unsaturated carboxylic acids under Swern oxidation conditions using dimethylsulfoxide, oxalyl chloride and triethylamine at low temperature.     

Micellar Mediated Halodecarboxylation of α,β‐Unsaturated Aliphatic and Aromatic Carboxylic Acids—A Novel Green Hunsdiecker–Borodin Reaction

A Novel Hunsdiecker‐Borodin reaction (HBR) has been carried out efficiently with α,β‐unsaturated aliphatic and aromatic carboxylic acids by using N‐halo succinimides such as N‐chloro succinimide (NCS), N‐bromo succinimide (NBS), and N‐iodo succinimide (NIS) under micellar media. The reaction with α,β‐unsaturated aromatic carboxylic acids afforded β‐halo styrenes in excellent yield while α,β‐unsaturated aliphatic carboxylic acids underwent decarboxylation and to give corresponding halo derivatives. The reactions are dramatically accelerated in micellar media. This procedure works efficiently in CTAB (cetyl trimethyl ammonium bromide), SDS (sodium dodecyl sulfate), and TX (Triton‐X‐100) media under stirred conditions at room temperature. At reflux temperatures the yield of reaction products were further enhanced from good to excellent.     

A four-component, one-pot synthesis of highly substituted 1,4-dihydro-1,8-naphthyridine-3-carboxamides

A new, one-pot, four-component reaction for the synthesis of a novel class of highly substituted 1,4-dihydro-1,8-naphthyridine-3-carboxamide derivatives starting from readily available inputs including aliphatic or aromatic amines, diketene, aromatic aldehydes, and 2-aminopyridines in the presence of a catalytic amount of p-toluenesulfonic acid under mild reaction conditions and in good yields at ambient temperature is described.     

Imination of N-methylazinium salts by liquid ammonia/potassium permanganate

Treatment of 1-methylquinolinium-, 1,4-dimethylquinolinium- and 1-methyl-1,X-naphthyridinium iodides (X = 5,8) with liquid ammonia/potassium permanganate leads to introduction of the imino group at C-2 forming the 1,2-dihydro-2-imino-1-methylquinolines and 1,2-dihydro-2-imino-1-methyl-1,X-naphthyridines (X = 5,8) respectively. 1,2-Dimethylquinolinium iodide, when subjected to treatment with liquid ammonia/potassium permanganate undergoes an oxo-demethylation reaction, yielding 1-methylquinol-2-one. The nmr-measurements of solutions of the above-mentioned salts in liquid ammonia clearly show the formation of a σ-adduct, strongly suggesting that these σ-adducts are intermediates in the imination reactions.     

Facile synthesis of 1H-pyrazolo[1,2-a]pyridazine-5,8-dione derivatives by a one-pot, three-component reactions

Protonation of the highly reactive 1:1 intermediate produced in the reaction between alkyl or aryl isocyanides and electron-deficient acetylenic esters with 3,6-dihydroxypyridazine, leads to a vinylisonitrilium cation, which undergoes an addition reaction with the conjugate base of the 3,6-dihydroxypyridazine to produce dialkyl 3-(alkyl or arylamino)-5,8-dioxo-5,8-dihydro-1H-pyrazolo[1,2-a]pyridazine-1,2-dicarboxylates in good yields at room temperature.     

Synthesis of 2-(4-amino substituted benzylidene) indanone analogues from aromatic nucleophilic substitution (SNAr) reaction

A novel, efficient and convenient procedure has been developed for the synthesis of 2-(4-amino-substituted benzylidene)indanone derivatives. In the first step, the reaction of 4-fluorobenzaldehyde with 5, 6-dimethoxy-2, 3-dihydro-1H-inden-1-one in the presence of NaOH in EtOH was described. In the next step, a variety of aliphatic and aromatic amines were reacted with 2-(4-fluorobenzylidene)-5, 6-dimethoxy-2, 3-dihydro-1H-Inden-1-one via aromatic substitution (S_NAr) reaction to produce 2-(4-aminobenzylidene)-5, 6-dimethoxy-2, 3-dihydro-1H-Inden-1-one derivatives as a novel class of 1-indanones. These products have been successfully prepared in good to excellent yields. ^1?H and ^13?C NMR, FT-IR spectroscopy and CHN analysis supported the proposed structures of the products.     

Highly enantioselective additions of diethylzinc to aldehydes using 2-triflamido-methyl-2'-hydroxy-1,1'- binaphthyl

[reaction: see text] A new N-triflated amino alcohol-titanium catalyst was designed for the asymmetric ethylation of aldehydes. This binaphthyl-based sulfonamido alcohol ligand shows uniformly high yield and enantioselectivity in the diethylzinc additions of aromatic, aliphatic, and unsaturated aldehydes.     

One pot synthesis of unsymmetrical dihydropyridines by green,catalyst free and environmentally benign protocol

Abstract

A facile and ecofriendly synthesis of β-enamino esters is reported by reaction of both aliphatic and aromatic amines with β-keto esters by refluxing in ethanol in absence of any catalyst. Addition of α,β-unsaturated aldehydes to the reaction mixture leads to the formation of unsymmetrical dihydropyridine derivatives which generally are metal free hydrogen sources for asymmetric reduction reactions.     

Kinetics of catalytic Meerwein-Ponndorf-Verley reduction of aldehydes and ketones using boron triethoxide

Catalytic Meerwein-Ponndorf-Verley (MPV) reduction of various aliphatic, aromatic, and unsaturated aldehydes and ketones to corresponding alcohols (analyzed by GC-MS) in the presence of boron triethoxide (B(OEt)₃) were studied. Kinetics of this reduction reaction was also studied and the respective rate constants were determined. It was found that B(OEt)₃ catalyzes the reduction of aliphatic aldehydes and ketones to alcohols at room temperature while aromatic aldehydes and ketones were not reduced under the same conditions. In addition, MPV reduction using B(OEt)₃ was found to be chemoselective as unsaturated aldehydes and ketones afforded the corresponding alcohols without affecting unsaturated groups. The mechanism proposed involves a six-membered transition state in which both the alcohol and the carbonyl are coordinated to the same boron centre of a boron alkoxide catalyst.     

Synthesis of 5-trifluoromethyl-5,8-dideazafolic acid and 5-trifluoromethyl-5,8-dideazaisofolic acid

The target folate analogue 5-trifluoromethyl-5,8-dideazafolic acid has been elaborated in a seven-step reaction sequence beginning with 2-fluoro-6-trifluoromethylbenzonitrile. The bridge-reversed isomer 5-trifluoromethyl-5,8-dideazaisofolic acid was prepared in six steps using the common intermediate 2,6-diamino-3,4-dihydro-4-oxo-5-trifluoromethylquinazoline. The key intermediate 2-amino-3,4-dihydro-4-oxo-5-trifluoromethyl-quinazoline was prepared using two distinct synthetic routes and the resulting products were found to be identical.     

Synthesis,spectroscopic studies and the mechanism of formation of 4,5-dihydro-1,2,4-oxadiazoles

Nine 4,5-dihydro-1,2,4-oxadiazoles, 2a-i , were synthesized by the reaction of benzamidoximes, 1a-i , with aliphatic and aromatic aldehydes. None of these compounds were encountered in the literature. The ultraviolet, infrared and proton magnetic resonance spectral studies supported the cyclic structure. Structure determination of a chloral-benzamidoxime adduct, 15 , by X-ray crystallography helped us to suggest the mechanism of formation of 4,5-dihydro-1,2,4-oxadiazole from benzamidoxime and an aldehyde. Substances 2a,b,d,e,g,h , showed some activity against fungus Neurospora crassa. Compound 2e also presented growth inhibition in Mycobacterium smegmatis.     

An unusual regiochemistry of reactions of a cyclohexenylphosphonate bearing a β-ethoxycarbonyl group with aldehydes

Reactions of lithiated ethyl 6-(dimethoxyphosphoryl)cyclohex-1-enecarboxylate with aliphatic, aromatic, and unsaturated aldehydes were studied and determined to proceed with α or δ regioselectivity. Such an unusual regioselectivity results from the contribution of two allylic carbanions: one, stabilized by the phosphonate moiety and the other stabilized by the carboethoxy group. The course of the reaction depends mainly on the structure of the aldehyde and the reaction conditions. The products of Horner-Wadsworth-Emmons reaction, including an analogue of some retinol metabolites, were formed under kinetic conditions whereas the δ-adducts were obtained as thermodynamic products.     

Synthesis of 5,8-dihydro-5-oxo-2-(3- or 4-pyridinyl)-pyrido[2,3-d]pyrimidine-6-carboxylic acids and the reinvestigation of the thermal cyclization of diethyl (2-hydroxy-4-pyrimidinyl)amino-methylenemalonate

Diethyl [2-(3- or 4-pyridinyl)-4-pyrimidinyl]aminomethylenemalonates 5 prepared by the reaction between 2-(3- or 4-pyridinyl)-4-pyrimidinamines 3 and diethyl ethoxymethylenemalonate ( 4 ) were thermally cyclized to afford ethyl 5,8-dihydro-5-oxo-2-(3- or 4-pyridinyl)pyrido[2,3-d]pyrimidine-6-carboxylates 6 . The later were alkylated with ethyl iodide and then saponified to give 5,8-dihydro-8-ethyl-5-oxo-2-(3- or 4-pyridinyl)pyrido-[2,3-d]pyrimidine-6-carboxylic acids 2 . Thermal cyclization of diethyl (2-hydroxy-4-pyrimidinyl)amino-methylenemalonate ( 8 ) gave ethyl 1,6-dihydro-4,6-dioxo-4H-pyrimido[1,6-a]pyrimidine-3-carboxylate ( 10 ) instead of ethyl 5,8-dihydro-2-hydroxy-5-oxopyrido[2,3-d]pyrimidine-6-carboxylate ( 9 ) as previously claimed.     

Bromine Complexes of Polyvinylpyrrolidone Supports: A Mild Reagent for the Transformation of α‐Oxoketene Dithioacetals to β‐Oxothiolesters

When α‐oxoketene dithioacetals 1a–n were treated with the bromine complex of a copolymer of 1‐vinyl‐2‐pyrrolidone and 4‐vinylpyridine, the corresponding thiolcarboxylates 2a–n were formed in excellent yields. The reaction also works with other 1‐vinyl‐2‐pyrrolidone‐derived polymers as well as commercially available polyvinylpyrrolidone–bromine complexes. The method is suitable for preparing aliphatic, aromatic, and γ,δ‐unsaturated β‐oxothiolcarboxylates.     

Catalytic asymmetric borylative aldol reaction of 5,6-dihydro-2H-pyran-2-one and ketones

A copper(I)-catalyzed asymmetric borylative aldol reaction of 5,6-dihydro-2H-pyran-2-one and simple ketones (including aromatic ketones and an aliphatic ketone) was disclosed, which afforded a series of chiral diols after an oxidative work-up in moderate yields with moderate to high diastereoselectivity and excellent enantioselectivity. The lactone moiety was easily opened with methanol to generate a chiral triol in moderate yield.     

A new synthesis of 3,6-dialkyl,diaryl and diheterocyclic-1,2-dihydro-l, 2,4,5-tetrazines

Some 3,6-dialkyl, diaryl and diheterocyclic-1,2-dihydro-1,2,4,5-tetrazines have been synthesized from the action of hydrazine on aliphatic selenonesters, and aromatic and heterocyclic selenoamides.     

Studies on quinones. Part 25. Synthetic approaches to 6,9-dioxygenated-benzazepinones

The Schmidt and Beckmann rearrangement of 3,4-dihydro-4,4-dimethyl-1(2H)-naphthalenones bearing oxygenated groups at the 5,8-positions, and some of their oximes are reported. Depending upon the structure of the substrates and the reaction conditions 4,5-dihydro-3H-naphth[1,8-cd]isoxazol, benzazepin-2-one and 5,6-dihydro-7H-tetrazolo[1,5-a][2]benzazepine derivatives were generated.     

Nitration of 5,6,7,8-tetrahydro-5,8-methanoisoquinoline N-oxide with other aromatic substitutions. Isolation and mutagenicity of an α-nitropyridine N-oxide

Treatment of 5,6,7,8-tetrahydro-5,8-methanoisoquinoline N-oxide ( 2 ) with fuming nitric acid afforded 3-nitro-5,6,7,8-tetrahydro-5,8-methanoisoquinoline N-oxide ( 3 ), an example of formation of an α-nitropyridine N-oxide derivative by nitration of N-oxides. Further reaction of 3 resulted in deoxygenation giving 3-nitro-5,6,7,8-tetrahydro-5,8-methanoisoquinoline ( 4 ). No aromatic nitration was observed by similar treatment of 5,6,7,8-tetrahydro-5,8-methanoisoquinoline ( 1 ) or 5,6,7,8-tetrahydroisoquinoline N-oxide ( 11 ). Some other aromatic substitutions with 1 and 2 were caried out to obtain mainly the 3-substituted derivatives. Significant mutagenicity of 3 is briefly reported.     

Reaction of 1-methylthio-3,4-dihydroisoquinolines with amines

A study was carried out on the reaction of 1-methylthio-3,4-dihydroisoquinolines with aromatic and aliphatic amines, thiourea, semicarbazide, and thiosemicarbazide. The reactions with anthranilic acid and 2-amino-3-carboethoxy-4,5-dmeurylthiophene give 6,6-dmethyl-5,6-dihydro-8H-isoquino[1,2-blquinazolin-8-one and 6, 6, 9,10-tetramethyl-5,6-dihydro-8H-benzo[i]thieno[2,3-b]quinolizin-8-one, respectively. 1-Semicarbazido-and 1-thiosemicarbazido-3,4-dihydroisoquinolines were shown to undergo thermal elimination of ammonia to give substituted 1, 2, 4-triazolo [3, 4-a]isoquinolin-3-ones and 1, 2, 4-triazolo[3, 4-ajisoquinoline-3-thiones.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 800-806, June, 1996. Original article submitted June 19, 1995; revision submitted March 14, 1996.