Photochemical and thermal cyclizations of 4-(2-azidophenyl)-3,4-dihydropyrimidin-2-ones for the synthesis of 4-methylenepyrimidino[5,4-b]indol-2-ones

Photochemical and thermal cyclization of 4-(2-azidophenyl)-3,4-dihydropyrimidin-2-ones could afford fused indoles, such as 1,2,3a,9b-tetrahydro-4-methylenepyrimidino[5,4-b]indol-2-ones and 1,3,5,6,7a,12b-hexahydroquinazolino[9,4-b]indol-2,7-dione in high yields via nitrene electrophilic addition and rearrangement reactions.     

Palladium-catalyzed synthesis of 4-alkoxycarbonyl-3,4-dihydroisoquinolin-1(2H)-ones

Palladium-catalyzed intermolecular cyclocarbonylation of diethyl (2-iodoaryl)malonates with N-tosylimines produces 4-ethoxycarbonyl-3,4-dihydroisoquinolin-1(2H)-ones in moderate to good yields. This reaction is highly stereoselective. This protocol involves Mannich addition, and subsequent cyclocarbonylation.     

Synthesis of 3,4-dihydrobenzo[g]isoquinoline-1(2H)-ones and 3,4-dihydroisoquinoline-1(2H)-ones skeleton via intramolecular electrophilic cyclization

An original alternative approach to isoquinolines based on the installation of a benzene nucleus on a performed heterocyclic ring. Synthesis of 3,4-dihydrobenzo[g]isoquinoline-1(2H)-ones and 3,4-dihydroisoquinoline-1(2H)-ones via intramolecular electrophilic cyclization of 3,4-disubstituted lactams is reported.     

Access to 4-substituted 3,4-dihydroquinolin-2(1H)-ones by an unusual radical cyclisation of a secondary amide

A novel route to 3,4-dihydroquinolin-2(1H)-ones involving two radical addition steps is reported, starting from readily accessible xanthates and N-aryl-3-butenamides.     

Indium-mediated regioselective mono-allylation of 1,5-dicarbonyl compounds and dehydrative cyclization to 2,3-dihydro-4H-pyran-4-ones and 3,4-dihydro-2H-[1,4]oxazines

An indium-mediated Barbier type mono-allylation of 1,5-dicarbonyl compounds and a subsequent acid-catalyzed dehydrative cyclization afforded 2,3-dihydro-4H-pyran-4-ones and 3,4-dihydro-2H-[1,4]oxazines.     

p-Sulfonic acid calixarenes as efficient and reusable organocatalysts for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones/-thiones

A new and efficient methodology is proposed for obtaining 3,4-dihydropyrimidin-2(1H)-ones/-thiones through Biginelli reactions. It is based on the use of less than the stoichiometric amount of p-sulfonic acid calixarenes as organocatalysts. A number of aromatic aldehydes as well as urea or thiourea can be employed for successfully synthesizing the corresponding Biginelli adducts. The described methodology is devoid of metal-containing catalysts, which in turn is very attractive for safely producing 3,4-dihydropyrimidin-2-(1H)-ones/-thiones of pharmacological interest. In addition, the catalyst efficiency is not compromised after its successive use in reactions. This is the first report about the application of calixarenes as catalysts in the multicomponent Biginelli reaction.     

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.     

Cu(OTf)2: a reusable catalyst for high-yield synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Copper(II) triflate catalyzes efficiently the three-component condensation reaction of an aldehyde, β-ketoester and urea in acetonitrile to afford the corresponding 3,4-dihydropyrimidin-2(1H)-ones in high yields. The catalyst exhibited remarkable reusable activity.     

An efficient bakers’ yeast catalyzed synthesis of 3,4-dihydropyrimidin-2-(1H)-ones

Bakers’ yeast (Saccharomyces cerevisiae) efficiently catalyzes the three-component Biginelli reaction of aldehydes, β-keto esters, and urea/thiourea to form 3,4-dihydropyrimidin-2-(1H)-ones in good to excellent yields.     

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.     

Synthesis of chromeno[3,4-b]pyrrol-4(3H)-ones by cyclocondensation of 1,3-dicarbonyl compounds with 4-chloro-3-nitrocoumarin

The base-mediated cyclocondensation of 1,3-dicarbonyl compounds with 4-chloro-3-nitrocoumarin provides a convenient approach to various chromeno[3,4-b]pyrrol-4(3H)-ones.     

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.     

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.     

Synthesis of 2-Trihalomethyl-3,4-dihydrothieno[2,3-d]pyrimidin-4-ones

At room temperature, N-(1-chloro-2,2,2-trihaloethylidene)-O-methyl urethanes react with 2-aminothiophenes to form N-(2-thienyl)-N'-(methoxycarbonyl)trihaloacetamidines, which when heated in boiling toluene undergo ring closure to form 2-trihalomethyl-3,4-dihydrothieno[2,3-d]pyrimidin-4-ones.     

Propane phosphonic acid anhydride: a new promoter for the one-pot Biginelli synthesis of 3,4-dihydropyrimidin-2(1H)-ones

Propane phosphonic acid anhydride has been found to promote the Biginelli synthesis of 3,4-dihydropyrimidin-2(1H)-ones. The use of this agent is characterized by moderate costs, low toxicity and simple workup conditions.     

Traceless solid-phase synthesis of 1,4-disubstituted-6-nitro-3,4-dihydro-1H-quinoline-2-ones

A traceless solid-phase route to 1,4-disubstituted-6-nitro-3,4-dihydro-1H-quinazolin-2-ones is described. N-Alloc-3-amino-3-(2-fluoro-5-nitrophenyl)propionic acid was tethered to Rink resin via its carboxylic group. The protected amine was coupled with an organic acid after Alloc-deprotection and the arylfluorine was displaced with a primary amine to generate a resin-bound aniline with two diversity points. The aniline was released via cleavage to produce the desired products in high yield and purity.     

Biginelli reaction in aqueous medium: a greener and sustainable approach to substituted 3,4-dihydropyrimidin-2(1H)-ones

An environmentally benign aqueous Biginelli protocol for the synthesis of substituted 3,4-dihydropyrimidin-2(1H)-ones using polystyrenesulfonic acid (PSSA) as a catalyst has been achieved. These microwave-assisted reactions proceed efficiently in water in the absence of organic solvent, with simple filtration as the product isolation step.     

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.     

N1,N3-Diacyl-3,4-dihydropyrimidin-2(1H)-ones: neutral acyl group transfer reagents

Readily available N1,N3-diacyl-3,4-dihydropyrimidin-2(1H)-ones efficiently acylate ammonia, primary and secondary amines to furnish primary, secondary and tertiary amides in good to excellent yields. The wide applicability of the procedure is demonstrated by running the reactions in a neutral medium, easy isolation of products, recycling of the innocuous by-product and chemoselectivity of the transformation.     

Synthesis of 4-Alkynyl-substituted 3,4-Dihydropyrimidin-2(1H)-ones

4-Alkynyl-3,4-dihydropyrimidin-2-(1H)-ones were synthesized by a one-pot reaction of propynals, ethyl acetoacetate, and urea. The yields of acetylenic dihydropyrimidinones depend significantly upon the propynal structure and catalyst type. A comparative study of the catalysts revealed an important advantage of polyphosphate ester in tetrahydrofuran in comparison with hydrochloric acid in methanol or trimethylchlorosilane in dimethylformamide, allowing the preparation of target compounds in good or moderate yields.