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.     

Reaction between isocyanides and dialkyl acetylenedicarboxylates in the presence of strong CH-acids: one-pot synthesis of highly functionalized annulated 4H-pyrans

The highly reactive 1:1 adduct, produced from the reaction between dialkyl acetylenedicarboxylates and alkyl isocyanides, was trapped by strong cyclic CH-acids such as 4-hydroxy-6-methyl-2H-pyran-2-one or 4-hydroxycoumarin to yield dialkyl 2-(alkylamino)-5-oxo-4H,5H-pyrano[3,2-c]chromene-3,4-dicarboxylates or dialkyl 7-methyl-2-(alkylamino)-5-oxo-4H,5H-pyrano[4,3-b]pyran-3,4-dicarboxylates in good yields at room temperature.     

An improved synthesis of Biginelli-type compounds via phase-transfer catalysis

3,4-Dihydropyrimidin-2(1H)-one, 3,4-dihydropyrimidin-2(1H)-thione, and 3,4-dihydropyrimidin-2(1H)-imine derivatives were synthesized by modified Biginelli cyclocondensation reaction in a time-efficient manner with near quantitative yields starting from appropriately substituted aromatic aldehyde, β-ketoester and either urea, thiourea or guanidine as constituent synthons using tetra-butyl ammonium bromide (TBAB) as catalyst for the first time.     

Substituent directed regioselective synthesis of 2-oxonicotonic acids and methyl nicotinates

An innovative synthesis of aryl tethered 1,2-dihydro-2-oxopyridine-3-carboxylic acids has been developed through nucleophile induced ring transformation of methyl 6-aryl-4-methylsulfanyl-2H-pyran-2-one-3-carboxylates using either cyanamide or arylamidine in excellent yields. Further, the reaction of methyl 6-aryl-4-methylsulfanyl-2H-pyran-2-one-3-carboxylates with formamidine acetate under analogous reaction conditions did not follow the same course of reaction and produced methyl nicotinate, regioselectively, in good yield. Decarboxylation of a 6-aryl-4-methylsulfanyl-1,2-dihydro-2-oxopyridine-3-carboxylic acid has been achieved by heating in PPA. The 4-methylsulfanyl substituent in 3 has also been oxidized to the corresponding methylsulfonyl group with m-chloroperbenzoic acid.     

Antimony trichloride catalyzed three-component reaction of urea, aldehydes and cyclic enol ethers: a novel route to 4-arylhexahydrofuro[2,3-d]pyrimidin-2(3H)-ones

Antimony trichloride efficiently catalyses diastereoselective three-component reaction of urea, aromatic aldehydes and 2,3-dihydrofuran or 3,4-dihydro-2H-pyran leading to 4-arylhexahydrofuro[2,3-d]pyrimidin-2(3H)-ones and 4-arylhexahydro-1H-pyrano[2,3-d]pyrimidin-2(8aH)-ones, respectively in good yield.     

Biginelli reaction starting directly from alcohols

An efficient of one-pot oxidative access to 3,4-dihydropyrimidin-2-(1H)-ones directly from aromatic alcohols under mild conditions is reported. The protocol involves 1-methylimidazolium hydrogen sulphate [Hmim]HSO₄ catalyzed oxidation of aromatic alcohols to aromatic aldehydes with NaNO₃ followed by their cyclocondensation with 1,3-dicarbonyl compounds and urea in the same reaction vessel at 80 °C within 2-4 h to afford 3,4-dihydropyrimidin-2-(1H)-ones in 55-97% overall yields. Thus, the present work utilizing alcohols instead of aldehyde in Biginelli reaction is a valid and green alternative to the classical synthesis of 3,4-dihydropyrimidin-2-(1H)-ones.     

Synthesis of bis(arylcarbonylamino-1H-benzimidazol-5-yl) ethers

A procedure has been developed for the synthesis of bis(arylcarbonylamino-1H-benzimidazol-5-yl) ethers by reaction of the corresponding substituted benzoyl chloride with sodium cyanamide, followed by treatment of the resulting N-cyanobenzamide with 4-(3,4-diaminophenoxy)benzene-1,2-diamine in acid medium.     

Synthesis and Structure of Di[methoxy(ethoxy)carbonylamino-1<Emphasis Type="Italic">H</Emphasis>-benzimidazol-5-yl] Ethers

A procedure was developed for preparing di[methoxy(ethoxy)carbonylamino-1H-benzimidazol-5-yl] ethers by the reaction of methyl or ethyl chloroformate with sodium cyanamide, followed by the reaction of the resulting methyl or ethyl cyanocarbamate with 4-(3,4-diaminophenoxy)-1,2-phenylenediamine in acidic solution.     

Substituent dependent regioselective synthesis of pyranopyrandiones and 1,2-teraryls from 2H-pyran-2-ones

The one-pot substituent-directed regioselective synthesis of 1,7-diaryl-2-methyl-4H,5H-pyrano[3,4-c]pyran-4,5-diones 3 as the major and 3,4-diaryl-2-methyl-6-methylsulfanylbenzonitriles 4 as the minor products has been delineated through ring transformation of suitably functionalized 2H-pyran-2-ones 1 with aryl acetones 2. Under similar reaction conditions, 6-aryl-4-sec-amino-2H-pyran-2-ones 5 led, regioselectively, to 3,4-diaryl-2-methyl-6-sec-aminobenzonitriles 6.     

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).     

Unprecedented InCl3-catalyzed formation of cis-fused perhydrofuro[2,3-b]oxepines

2-Methylindole and its N-substituted derivatives react smoothly with 2,3-dihydrofuran (DHF) in the presence of a catalytic amount of InCl₃ under mild conditions to afford the corresponding 2-methyl-3-perhydrofuro[2,3-b]oxepin-4-yl-1H-indole derivatives in fairly good yields with high diastereoselectivity, while 3,4-dihydro-2H-pyran (DHP) affords exclusively 5,5-di(1H-3-indolyl)-1-pentanol derivatives in high yields under similar reaction conditions.     

1,3-Dipolar cycloaddition of β-alkoxyvinyl trifluoromethylketones with aryl (or benzyl) azides: Synthesis of 4-trifluoroacetylated 1H-1,2,3-triazoles

The 1,3-dipolar cycloaddition of aryl (or benzyl) azides with 1,1,1-trifluoro-4-ethoxy-3-butene-2-one proceeded smoothly by heating without solvent. 1-Aryl (or benzyl)-4-trifluoroacetyl-1H-1,2,3-triazoles were formed regiospecifically in good yield. These compounds were readily hydrated when exposed to air. In contrast, the reaction of benzyl azide with 4-trifluoroacetyl-2,3-dihydrofuran only gave minor amounts of 4-trifluoroacetyl-5-benzylamino-2,3-dihydrofuran in addition to an inseparable mixture of other products. 5-Trifluoroacetyl-3,4-dihydro-2H-pyran was inert towards benzyl azide under the same conditions.     

A new approach to N-3 functionalized 3,4-dihydropyrimidine-2(1H)-ones with 1,2,4-oxadiazole group as amide isostere via ionic liquid-phase technology

New N-3 functionalized 3,4-dihydropyrimidine-2(1H)-ones with 1,2,4-oxadiazole group as amide isostere were synthesized in six steps by ionic liquid-phase organic synthesis (IoLiPOS) methodology from ILP bound acetoacetate. The 3,4-dihydropyrimidine-2(1H)-one (3,4-DHPM) core was prepared in the first step by one-pot three-component Biginelli condensation followed by N-alkylation with chloroacetonitrile. Then the nitrile group appended on the 3,4-DHPM heterocycle was quantitatively transformed into amidoxime. Addition of aliphatic carboxylic anhydride or aromatic carboxylic acid to the amidoxime produced the expected 1,2,4-oxadiazole via the O-acylamidoxime intermediate grafted on the ILP bound 3,4-DHPM using two convergent methods. After cleavage by transesterification under mild conditions, the target compounds were obtained in good overall yields. The structures and the purities of the reaction intermediates in each step were verified easily by routine spectroscopic analysis.     

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.     

Regioselective synthesis of cytotoxic 4-(1-alkynyl)-substituted 2-(5H)-furanones

4-(1-Alkynyl)-3-bromo- and 4-(1-alkynyl)-3-chloro-2(5H)-furanones have been regioselectively synthesized in moderate to good yields by a new version of the Pd/Cu-catalyzed Sonogashira reaction involving treatment of 1-alkynes with 3,4-dibromo- and 3,4-dichloro-2(5H)-furanone, respectively, in the presence of KF as a base. 4-(1-Alkynyl)-3-bromo-2(5H)-furanones have been found to be able to undergo Stille-type and Suzuki-type reactions with aryl(tributyl)tins and arylboronic acids, respectively, to give 4-(1-alkynyl)-3-aryl-2(5H)-furanones in modest to satisfactory yields. Some 4-(1-alkynyl)-substituted 2(5H)-furanones so prepared have been found to exhibit significant cytotoxic activities, especially against human leukemia cell lines.     

ZrCl4 or ZrOCl2 under neat conditions: optimized green alternatives for the Biginelli reaction

Biginelli reactions were performed using either ZrCl₄ or ZrOCl₂·8H₂O as catalysts under neat conditions. Shorter reaction time than most of the classical methods was required when ZrCl₄ was used. In general, 3,4-dihydropyrimidin-2(1H)-ones and thioxo-3,4-dihydropyrimidin-2(1H)-ones were obtained under neat conditions in moderate to good yields and good purity without using harmful solvents in the work up.     

Diketene as an alternative substrate for a new Biginelli-like multicomponent reaction: one-pot synthesis of 5-carboxamide substituted 3,4-dihydropyrimidine-2(1H)ones

5-Carboxamide substituted 3,4-dihydropyrimidine-2(1H)one derivatives were synthesized in a simple and efficient method from the one-pot four-component reactions of an aliphatic or aromatic amine, diketene, an aromatic aldehyde and urea or thiourea in the presence of p-toluenesulfonic acid as a catalyst under mild reaction conditions at ambient temperature.     

Regioselective dehydrogenation of 3,4-dihydropyrimidin-2(1H)-ones mediated by ceric ammonium nitrate

Ceric ammonium nitrate (CAN) has been explored for the regioselective oxidation of 3,4-dihydropyrimidin-2(1H)-ones (DHPMs). Interestingly, we obtained ethyl 2,4-dioxo-6-phenyl-tetrahydropyrimidin-5-carboxylates as the major products during the oxidation of DHPMs by CAN/AcOH at 80 °C. The reaction afforded a mixture of products while employing CAN in organic solvents without additives. However, the regioselective dehydrogenated product, ethyl 6-methyl-4-aryl(alkyl)-pyrimidin-2(1H)-one-5-carboxylate was obtained by performing the reaction with NaHCO₃. The single crystal X-ray crystallography of ethyl 6-methyl-4-(2-phenyl)-pyrimidin-2(1H)-one-5-carboxylate revealed that the oxidized product existed in amidic form rather than aromatized enol form of pyrimidines. The efficiency of the present protocol enabled the synthesis of structurally diverse pyrimidines in moderate to good yields under milder reaction conditions.     

The reaction of 2-(1-hydropolyfluoro-1-alkenyl)-4H-3,1-benzoxin-4-ones with dinucleophilic reagents: a convenient route to fluoroalkylated nitrogen-containing tricyclic compounds

The reactions of 2-(1-hydropolyfluoro-1-alkenyl)-4H-3,1-benzoxin-4-ones (2) with hydrazine hydrate and phenyl hydrazine were investigated. The reaction of 2 with hydrazine hydrate in ethanol under reflux condition readily gave 2-fluoroalkyl-4H-pyrazolo[5,1-b]quinazolin-9-ones (3) in high yields. The reaction of 2 with phenyl hydrazine, however, resulted in the formation of 2-(2-phenyl-5-fluoroalkyl-2H-pyrazol-3-yl) benzoic acids (7). Further treatment of 7 with PPA gave 1-phenyl-4,9-dihydro-3-fluoroalkyl-1H-pyrozolo[3,4-b]quinolin-4-ones (4) in 65-80% overall yields.     

Highly diastereoselective cycloaddition reactions of variously substituted 1-thia- and 1-thia-3-aza-buta-1,3-dienes. Synthesis of enantiomerically pure 5,6-dihydro-4H-[1,3]thiazines and 3,4-dihydro-2H-thiopyrans

The cycloaddition of 2- or 2,3-substituted 1-thia- and 1-thia-3-aza-4-dimethylamino-buta-1,3-dienes with various dienophiles in the presence of a Lewis acid provides a rapid and diastereoselective access to the 3,4-dihydro-2H-thiopyran and 5,6-dihydro-4H-[1,3]thiazine backbones. The generally observed trans relationship between the two newly created strereogenic centres was demonstrated to be the expression of a thermodynamic control of the reaction. The use of chiral dienophile derived from chiral oxazolidin-2-ones allowed us to prepare enantiopure 5,6-dihydro-4H-[1,3]thiazines and 3,4-dihydro-2H-thiopyrans. In the asymmetric synthetic process the chiral auxiliary removal step was best accomplished in the presence of samarium triflate in methanol.