Pyrolytic desulfurization ring contraction of condensed thiadiazines as a general route towards pyrazoloazines and pyrazoloazoles with a bridgehead (ring junction) nitrogen atom

Pyrolytic conversion of [1,2,4]triazino[3,4-b][1,3,4]thiadiazin-4-ones, [1,3,4]thiadiazino[2,3-b]quinazolin-10-ones and [1,2,4]triazolo[3,4-b][1,3,4]thiadiazines into their corresponding pyrazolo[5,1-c][1,2,4]triazin-4-ones, pyrazolo[4,3-b]quinazolin-9-ones and pyrazolo[5,1-b][1,2,4]triazoles via desulfurization ring contraction is described. The starting condensed 1,3,4-thiadiazines were prepared from the corresponding readily available 4-amino-3-thioxo-1,2,4-triazin-5(4H)-ones, 3-amino-2,3-dihydro-2-thioxoquinazolin-4(1H)-one and 4-amino-3(2H)-thioxo-1,2,4-triazoles upon reaction with the appropriate α-haloketones in two steps, or directly in one step in ethylpyridinium tetrafluoroborate (ionic liquid, IL).     

2-Cyanopyridazin-3(2H)-ones: effective and chemoselective electrophilic cyanating agents

2-Cyanopyridazin-3(2H)-ones are novel, effective, selective and electrophilic cyanating agents. A variety of amino, thiol and carbon nucleophiles are chemoselectively N-, S- or C-cyanated in excellent yield using 2-cyanopyridanzin-3(2H)-ones in water or tetrahydrofuran.     

An efficient HCCP-mediated direct amination of quinazolin-4(3H)-ones

An efficient direct amination of quinazolin-4(3H)-ones has been developed. Treatment of quinazolin-4(3H)-ones with HCCP, DIPEA, and N-contained nucleophiles in acetonitrile could be able to form the corresponding 4-aminoquinazoline derivatives. Under the optimal reaction conditions, the amination products were achieved in good yields.     

A new approach to the synthesis of 4-(N-aryl)carbamoylmethyl-4,5-dihydropyridazin-3(2H)-ones

Reaction of N-aryl substituted maleimides with aliphatic ketazines leads to the formation of 4,5-dihydropyridazin-3(2H)-ones in moderate yields. The reaction proceeds through 1,4-addition of an azine to the maleimide double bond, as confirmed by separation of the corresponding adducts in some cases, which are then converted into 4,5-dihydropyridazin-3(2H)-ones. In addition, the solid-state synthesis of 4,5-dihydropyridazin-3(2H)-ones is demonstrated for the first time.     

Superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids: synthesis of quinolin-2(1H)-one derivatives

The superelectrophilic activation of N-aryl amides of 3-arylpropynoic acids by Bronsted superacids (CF₃SO₃H, HSO₃F) or strong Lewis acids AlX₃ (X=Cl, Br) results in the formation of 4-aryl quinolin-2(1H)-ones in quantitative yields. The vinyl triflates or vinyl chlorides may be formed as additional reaction products. The investigated amides in reactions with benzene give 4,4-diaryl 3,4-dihydroquinolin-2-(1H)-ones under the superelectrophilic activation. 4-Aryl quinolin-2(1H)-ones in POCl₃ are converted into 4-aryl 2-chloroquinolines. 4-Fluorophenyl-4-phenyl 3,4-dihydroquinolin-2-(1H)-one give N-formylation products in a yield of 79% under the Vilsmeier–Haack reaction conditions.     

Application of N,3-diaryl-3-oxo-propanethioamide in synthesis: an efficient and mild domino approach to highly substituted fused chromenones

A convenient and rapid synthesis of hitherto unknown 3-aroyl-4-aryl-2-phenylamino-4H-benzo[g]chromene-5,10-diones in high yield from β-aroyl-thioacetanilide, aromatic aldehyde, and 2-hydroxy-1,4-naphthoquinone via InCl₃ catalyzed one-pot three-component tandem Knoevenagel condensation–Michael addition–intramolecular cyclization–elimination reaction sequence is disclosed for the first time. This domino protocol has been used to obtain highly substituted pyrano[3,2-c]chromen-5(4H)-ones and 7,7-dimethyl-7,8-dihydro-4H-chromen-5(6H)-ones from N,3-diaryl-3-oxo-propanethioamide, aromatic aldehyde, and 4-hydroxycoumarine or dimedone under mild reaction conditions. A plausible reaction mechanism is proposed. The 4H-pyrano[3,2-c]chromen-5-one and 7,7-dimethyl-7,8-dihydro-4H-chromen-5(6H)-one derivatives possessing 3-(2-chlorobenzoyl)-2-phenylamino-substituents further cyclized under basic conditions to yield penta-cyclic 7,13-diaryl-5,14-dioxa-13-aza-benzo[a]naphthacen-6,8(7H,13H)-dione and tetra-cyclic 6,12-diaryl-3,3-dimethyl-3,4-dihydro-2H-chromeno[2,3-b]quinolin-1,11(6H,12H)-dione, respectively.     

2-Pivalamido-3H-pyrimidin-4-one derivatives: convenient pivalamide hydrolysis using Fe(NO3)3 in MeOH

A simple methodology for pivalamide (trimethylacetamide, pivaloylamino) hydrolysis has been discovered using Fe(NO₃)₃ in MeOH at room temperature. The pivalamido group of 2-pivalamido-3H-pyrimidin-4-ones or fused 2-pivalamido-3H-pyrimidin-4-ones such as 2-pivalamido-3H-quinazolin-4-ones and 2-pivalamido-3H-pteridines have been hydrolysed under these conditions to afford the corresponding amine.     

Rapid access to 3-(N-substituted)-aminoquinolin-2(1H)-ones using palladium-catalyzed C-N bond coupling reaction

A series of 3-(N-substituted)-aminoquinolin-2(1H)-ones have been synthesized by the palladium-catalyzed C-N coupling reaction starting from 3-bromoquinolin-2-(1H)-ones. Various nucleophiles including amines, amides, sulfonamides, carbamates and ureas have been used successfully. In all the cases, the reactions take place rapidly in 1,4-dioxane and proceed in good to excellent yield using palladium acetate as a catalyst, Xantphos as a ligand and Cs₂CO₃ as a base.     

Single step synthesis of 2,3-dialkyl-6-nitro-quinazolin-4(3H)-imines and 3,5-dialkyl-9-nitro-imidazo[1,2-c]quinazolin-2(3H)-ones

A single step synthesis of 2,3-dialkyl-6-nitro-quinazolin-4(3H)-imines and 3,5-dialkyl-9-nitro-imidazo-[1,2-c]-quinazolin-2(3H)-ones from simple carbonyl compounds, primary amines or amino acid methyl esters and 2-azido-5-nitro-benzonitrile was developed. Key intermediates were N,N′-disubstituted amidines obtained by rearrangement of 4,5-dihydrotriazoles; the new heterocyclic rings were formed by spontaneous intramolecular reaction of the amino and cyano groups which are present in the intermediates.     

Efficient N-arylation of pyridazin-3(2H)-ones

A variety of substituted pyridazin-3(2H)-ones are directly N-arylated in good yield using lead tetraacetate/zinc chloride in benzene or in substituted benzenes including chloro- and bromobenzene.     

Synthesis of furo[2,3-b]pyridin-4(7H)-ones and related quinolinone via Brønsted acid-promoted cyclisation of alkynes

N-Alkyl-4-alkoxy-3-alkynylpyridin-2(1H)-ones readily undergo acid-promoted 5-endo-heteroannulation to furopyridinium intermediates that are dealkylated in situ to provide the corresponding furo[2,3-b]pyridin-4(7H)-ones. The same strategy applies to the formation of furo[2,3-b]quinolin-4(9H)-ones. In the case of Me₃Si-substituted alkynes, hydration of the triple bond was observed.     

Isoquinolin-1(2H)-ones and 1,6-naphthyridin-5(6H)-ones by an N-acylation-SNAr sequence

A new synthesis of 2,3-dialkyl-4-carbomethoxyisoquinolin-1(2H)-ones and 6,7-dialkyl-8-carbomethoxy-1,6-naphthyridin-5(6H)-ones is reported. The process involves treatment of a β-enaminoester with 2-fluoro-5-nitrobenzoyl chloride, 2-fluorobenzoyl chloride or 2-chloronicotinoyl chloride followed by heating in the presence of base. The conversion, which proceeds by an N-acylation-S_NAr reaction sequence, affords 50–86% yields when R¹ is n-alkyl but ≤30% yields when R¹ is α-branched.     

Synthesis of N-substituted 1,2,3,4-tetrahydrobenz[g]isoquinoline-5,10-diones

The synthesis of 1,2,3,4-tetrahydrobenz[g]isoquinoline-5,10-dione hydrochlorides is reported starting from 1,4-dihydrobenz[g]isoquinoline-3(2H)-ones or ethyl (3-aminomethyl-1,4-dimethoxynaphth-2-yl)acetates. A third strategy relies on the synthesis of the title compounds via an N-protected 2-(3-bromomethyl-1,4-dimethoxynaphth-2-yl)ethylamine. The synthesized 1,2,3,4-tetrahydro-benz[g]isoquinoline-5,10-diones are a new class of quinones, which have not been reported yet.     

Unexpected course of rearrangement of substituted S-(1(3H)-isobenzofuranone-3-yl)isothiuronium bromides

Three series of S-(1(3H)-isobenzofuranone-3-yl)isothiuronium bromides differing in substitution at the isothiuronium moiety (none, one or two methyl groups) and at the benzene ring were prepared and characterized. These salts were then treated with various bases (acetate, triethylamine, Na₂CO₃) to give either 1-hydroxy-3-oxo-1,3-dihydro-2H-isoindol-2-carbothioamides or the product of S to N isobenzofuranone-3-yl migration, i.e., 1,3-dimethyl-1-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)thioureas. If ammonia was used in reaction with N,N′-dimethyl isothiuronium salts then 3-hydroxy-2,3-dihydro-1H-isoindol-1-ones were formed together with 1,3-dimethyl-1-(3-oxo-1,3-dihydro-2-benzofuran-1-yl)thioureas in parallel reaction with the yields increasing with ammonia concentration. The formation of isoindolones takes place in two steps with an aldehyde intermediate, which can be trapped with N,N-dimethylhydrazine.     

Synthesis of novel glycosyl-1,2,3-1H-triazolyl methyl quinazolin-4(3H)-ones and their effect on GLUT4 translocation

Cu(OTf)₂ catalyzed synthesis of propargylated 2,3-dihydroquinazolin-4(1H)-ones has been accomplished from 2-amino-N-propargyl benzamides and aromatic aldehydes under MW irradiation. Next, a series of novel glycosyl triazolyl methyl quinazolin-4(3H)-ones have been synthesized by CuAAC reaction of propargylated 2,3-dihydroquinazolin-4(1H)-ones with glycosyl azides followed by iodine mediated oxidation. In this series, six compounds showed promising to significant GLUT4 translocation activity comparable to rosiglitazone.     

New synthetic methods for 2,3-diarylacridin-9(10H)-one and (E)-2-aryl-4-styrylfuro[3,2-c]quinoline derivatives

Two new synthetic methodologies for 2,3-diarylacridin-9(10H)-ones were developed. The first one involves the Heck reaction of (E)-3-iodo-2-styrylquinolin-4(1H)-ones with styrenes, leading to (E,E)-2,3-distyrylquinolin-4(1H)-ones, which when heated at high temperatures cyclize in two different ways. Electrocyclization and further in situ oxidation leads to 2,3-diarylacridin-9(10H)-ones, while tautomerization, cyclization by nucleophilic addition and further in situ oxidation produces (E)-2-aryl-4-styrylfuro[3,2-c]quinolines as the main compound. The second method gives only 2,3-diaryl-10-methylacridin-9(10H)-ones and involves the Heck reaction of (E)-3-iodo-1-methyl-2-styrylquinolin-4(1H)-ones and styrenes, leading to (E,E)-1-methyl-2,3-distyrylquinolin-4(1H)-ones, which when heated at high temperatures cyclize through electrocyclization and oxidation processes affording the expected compounds. The structures of all new compounds were established by extensive NMR studies.     

New cycloaddition reaction between 4-arylidene-2-phenyl-5(4H)-1,3-oxazolones and benzyne; facile synthesis of 1,4(H)-benzoxazepine-2-ones and their N-phenyl derivatives

Reaction of 4-arylidene-2-phenyl-5(4H)-1,3-oxazolones with benzyne afforded predominantly, 3-arylidene-7-hydroxy-7-phenyl-1,4(H)-benzoxazepine-2-ones in addition to their N-phenyl derivatives. However, the reaction of the target oxazolones with an excess of benzyne gave only the N-phenyl derivatives of 1,4(H)-benzoxazepine-2-ones in good yields. The reaction mechanism describing product formation is also explained. Arylation of 1,4(H)-benzoxazepine-2-ones with benzyne proceeded successfully to give the N-phenyl products.     

Visible-light-induced chemoselective reactions of quinoxalin-2(1H)-ones with alkylboronic acids under air/N2 atmosphere

A visible-light-induced chemoselective reactions of quinoxalin-2(1H)-ones with alkylboronic acids in the presence of air (O₂) and N₂ atmosphere was developed under transition-metal free conditions, providing 3-alkylquinoxalin-2(1H)-ones and 3,4-dihydroquinoxalin-2(1H)-ones, respectively. The overall strategy accommodates a broad scope of substituted quinoxalin-2(1H)-ones and alkylboronic acids with good to excellent product yields.     

A facile synthesis of chromeno[3,4-c]spiropyrrolidine-oxindoles via 1,3-dipolar cycloadditions

A facile one-pot synthesis of chromene bearing novel spiropyrrolidine-oxindoles has been accomplished by the [3+‏2]-cycloaddition reaction of 3-acetyl-2H-chromen-2-ones with azomethine ylides derived in situ from isatin or N-methyl isatin with sarcosine.     

Highly enantioselective α-sulfenylation of 5H-oxazol-4-ones to N-(sulfanyl)succinimides

An unprecedented asymmetric α-sulfenylation of 5H-oxazol-4-ones to N-(sulfanyl)succinimides has been established, to access various α-sulfenylated adducts with good to excellent enantioselectivities (86–95% ee) by utilizing a cinchona alkaloid-derived squaramide as catalyst. The conditions of this α-sulfenylation protocol simultaneously satisfy N-(arylthio)succinimides, N-(benzylthio)succinimides, and N-(alkylthio)succinimides by tuning the substituted groups of 5H-oxazol-4-ones on the 2-position as well as additives.