LiClO4-Catalyzed One-Pot Synthesis of Dihydropyrimidinones: An Improved Protocol for Biginelli Reaction

An Efficient Synthesis of 3,4-dihydro-2(1H)-pyrimidinones from Aldehyde Bisulfite Adducts using Recyclable Wang Resin Supported Sulfonic Acid Catalyst

Abstract:

An efficient one-pot multicomponent synthesis of 3,4- dihydropyrimidin-2(1H)-ones has been developed from aldehyde bisulfite adducts, ethyl acetoacetate and urea using recyclable polymer- supported sulfonic acid catalyst. This new method provides several advantages over the previous synthesis, including high product yields, commercially viable, minimal workup operations and sustainable chemical practices.

Efficient Synthesis of Dihydropyrimidines Using a Highly Ordered Mesoporous Functionalized Pyridinium Organosilica

A Brönsted acidic ionic solid pyridinium-functionalized organosilica network (PMO-Py-IL) was demonstrated to efficiently catalyse one-pot Biginelli condensation reaction. The green synthesis of 3,4-dihydro-2(H)-pyrimidinones (DHPMs) with high yield was carried out via one-pot three component condensation of β- dicarbonyls, aldehydes, and urea in the presence of a catalytic amount of PMO-Py-IL nanomaterial as an efficient nanocatalyst under solvent free conditions. Furthermore, the catalyst showed outstanding stability and could be easily separated and reused for at least ten reaction runs without significant loss of activity and product selectivity. The green protocol features simple set-up, cost-effectiveness, easy work-up, eco-friendly and mild reaction conditions.

Synthesis of dihydropyrimidinones via multicomponent reaction route over acid functionalized Metal-Organic framework catalysts

Multi component reactions over heterogeneous solid acid catalysts are extremely important owing to easy separation, amenable recycling, and prospective scaling up of the process. Here, we are reporting the synthesis of biologically important dihydropyrimidinones over postsynthetic modified Cr-based metal-organic framework materials as heterogeneous catalysts containing the bifunctional Lewis and Brønsted acid sites. Cr-based metal-organic frameworks contained coordinatively unsaturated metal sites as inherent Lewis acid sites, whereas postsynthetic modifications introduced the Brønsted acid sites in the framework. A direct one pot synthesis route was employed to produce the pristine MOF in pure aqueous medium without using any additives. The bulk structure, morphology, surface and bonding properties of the synthesized materials were thoroughly characterized with powder XRD, FTIR, XPS, FE-SEM, TGA, and N₂ sorption isotherms. A qualitative evolution of acid strength was carried out over the functionalized MOFs. Among the post synthetic functionalized materials, carboxylic acid functionalized framework exhibited a very high yield of dihydropyrimidinones under solvent less moderate reaction conditions. The catalyst also demonstrated a robust recyclability and wide substrate scope. Comparative study showed a very high catalytic activity of the postsynthetic modified MOFs in comparison to the reported literature. The reaction condition was optimized by varying parameters like solvent, temperature, reaction duration and catalyst loadings. The mechanistic studies indicated the involvement of both the Lewis and Brønsted sites acid sites of the catalysts in the multicomponent reaction.

Synthesis of Dihydropyrimidinones (DHPMs) and Hexahydro Xanthene Catalyzed by 1,4-Diazabicyclo [2.2.2] Octane Triflate Under Solvent-Free Condition

OBJECTIVE

DABCO salts were evaluated as catalysts for the Biginelli reaction between 4- methoxybenzaldehyde, urea and ethyl acetoacetate under solvent-free conditions. 1,4-Diazabicyclo [2.2.2] octane triflate was found to be a simple, inexpensive, highly efficient catalyst for Biginelli reaction for a variety aromatic aldehyde with urea and ethyl acetoacetate at 80°C afforded corresponding 3,4-dihydropyrimidinones in 50-99% yields after 30-120 minutes. 1,3-Cyclohexadione was used in place of ethyl acetoacetate in the absence of urea this methodology is giving hexahydro xanthene derivatives in good to excellent yields after 3-4 hours.

METHODS

DABCO salt 4 (5 mol%), 4-methoxybenzaldehyde (0.73 mmol) and urea (0.73 mmol) were stirred for 10 minutes at 80°C, then ethyl acetoacetate (1.5 equiv.) was added and reaction mixture was stirred at 80°C for specified time. The resulting solution was stirred continuously and progress of the reaction was followed by TLC. The crude reaction mixture was purified by flash column chromatography on silica gel (hexane/ethyl acetate (1:2)) to give pure desired product.

RESULTS

Reaction conditions of the Biginelli reaction were optimized using 4-methoxybenzaldehyde (0.73 mmol), urea (0.73 mmol), and ethyl acetoacetate (5 equiv.) as model substrates catalyzed by 1,4-Diazabicyclo [2.2.2] octane triflate (5 mol%) in a different solvents, screening of different catalysts and different temperatures. Neat condition was found to be the best for the Biginelli condensation and corresponding 3,4- dihydropyrimidinones was obtained in good to excellent yields. When the reaction was carried out with benzaldehyde derivatives and cyclohexane-1,3-dione in place of ethyl acetoacetate in the absence of urea, solely corresponding hexahydro xanthene derivatives were obtained in 61-91% yields.

CONCLUSION

In conclusion, we have applied salts of 1,4-Diaza-bicyclo [2.2.2] octane as catalysts in the Biginelli condensation and corresponding 3,4-dihydropyrimidinones were obtained in 50- 99% yields under solvent free conditions. This methodology is having advantages like simple work-up; low loading of catalyst and reaction was performed at moderate temperature under solvent-free conditions.

Phosphotungstic Acid Catalysed One-Pot Synthesis of 5-Alkoxycarbonyl-4-Aryl-3,4-Dihydropyrimidin-2-Ones

5-Alkoxycarbonyl-4-aryl-3,4-dihydropyrimidin-2-ones are synthesised by the one-pot reactions of aldehydes, β-ketoesters and urea using a catalytic amount of phosphotungstic acid (PTA) in ethanol. The modified Biginelli cyclocondensation not only shortens the reaction period and simplifies the operation, but also improves the yields.

One-Pot Construction 3,4-Dihydropyrimidin-2(1H)-Ones Catalysed by Samarium(III)

An efficient synthesis of dihydropyrimidin-2(1 H)-ones using samarium(III) nitrate hexahydrate as a catalyst from an aldehyde, 1,3-dicarbonyl compounds and urea under solventless conditions is described. Compared with the classical Biginelli reaction, the yields of this protocol increased from 20–50% to 78–98% while the reaction time was significantly shortened from 18 h to 15–30 min.

One-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones catalyzed by SO3H@imineZCMNPs as a novel, efficient and reusable acidic nanocatalyst under solvent-free conditions

The synthesis of 3,4-dihydropyrimidin-2(1H)-one derivatives was accomplished efficiently via a three-component reaction between ethyl acetoacetate, various types of aldehydes, and urea in the presence of 10 mg SO₃H@imineZCMNPs as a novel, environment friendly, and reusable heterogeneous magnetic nanocatalyst under solvent-free conditions at 90 °C. The desired products were obtained with high quantitative yields. The catalyst was separated by simple isolation from the reaction mixture using a permanent magnet and reused several times without any significant loss of catalytic activity. The synthesized catalyst was fully characterized through various techniques including thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and the Hammett acidity test. This methodology tolerates most substrates and has the salient features of green reaction conditions, lower catalyst loading, high quantitative yields, low cost, the absence of solvents, and easy isolation and reusability of the catalyst.

N-Donor ligand activation of titanocene for the Biginelli reaction via the imine mechanism

The remarkable activation of stable titanocene dichloride (Cp₂TiCl₂) was achieved using N-donor ligand urea in an alcoholic solvent, leading to the formation of a Ti(iv) species [(MeO)₂Ti(NHCONH₂)]⁺, the existence of which was verified by ESI-MS, ESI-MS/MS, and NMR. Catalyzed by the newly formed Ti(iv) species, a myriad of 3,4-dihydropyrimidin-2-(1H)-ones were produced via a three-component Biginelli reaction. Further mechanistic investigation indicated that the Biginelli reaction had taken place via the imine route.

Stable titanocene dichloride (Cp₂TiCl₂) was activated by the N-donor ligand urea to form [(MeO)₂Ti(NHCONH₂)]⁺, which catalyzed the Biginelli reaction to produce 3,4-dihydropyrimidin-2-(1H)-ones.

FeCl₃∙6H₂O/TMSBr-Catalyzed Rapid Synthesis of Dihydropyrimidinones and Dihydropyrimidinethiones under Microwave Irradiation

An efficient and practical protocol has been developed to synthesize dihydropyrimidinones and dihydropyrimidinethiones through FeCl₃∙6H₂O/TMSBr-catalyzed three-component cyclocondensation under microwave irradiation. This approach features high yields, broad substrate scope, short reaction time, mild reaction conditions, operational simplicity and easy work-up, thus affording a versatile method for the synthesis of dihydropyrimidinones and dihydropyrimidinethiones.

Highly effective Brønsted base/lewis acid cooperative catalysis: a new Cd metal–organic framework for the synthesis of Hantzsch 1,4-DHPs at ambient temperature

A new 3D metal–organic framework {[Cd₃(BDC)₃(OPP)(DMF)₂]·2DMA}_n (TMU-33) has been synthesized. The performance of the imine functional group of the OPP ligand as a Brønsted base and open Cd site as a Lewis acid in this framework was investigated as cooperative catalyst.

Efficient one-pot synthesis of 3,4-dihydropyrimidin-2(1H)-ones catalyzed by a new heterogeneous catalyst based on Co-functionalized Na+-montmorillonite

A facile and efficient solvent-free protocol for the synthesis of 3,4-dihydropyrimidin-2(1H)-ones by using Co@imine-Na⁺-MMT as a new, environmentally friendly and reusable heterogeneous catalyst is reported.

General solvent-free ionic liquid catalyzed C–N/C–C coupled cyclization to diverse dihydropyrimidinones and new organic materials: Langmuir–Blodgett film study

An ionic liquid catalyzed dual C–N/C–C coupled cyclization under solvent-free green conditions to DHPMs and their innovative new organic materials by LB film study are demonstrated.

A series of phenyl sulfonate metal coordination polymers as catalysts for one-pot Biginelli reactions under solvent-free conditions

A series of phenyl sulfonate metal coordination polymers have been obtained under hydrothermal conditions, which show high catalytic performances for one-pot Biginelli condensation reactions under solvent-free conditions.