BIFC and QFC promoted rapid and cleaner aromatization of 1,4‐dihydropyridines under solvent‐free condition

This communication expresses aromatisation of 1,4‐dihydropyridines to pyridine derivatives with the help of alumina supported benzimidazolium fluorochromate (BIFC) and quinolinium fluorochromate (QFC) as oxidants under solvent‐free microwave irradiation. Moderate to excellent yield (80‐98%) of pyridine derivatives were achieved by this methodology.     

Rapid and cleaner synthesis of 1,4‐dihydropyridines in aqueous medium

The present investigation deals with a novel water soluble Lewis acid complex, Zn[(L)proline]₂ catalyzed Hantzsch 1,4‐dihydropyridine derivatives syntheses in aqueous medium assisted by microwave irradiation. The microwave promoted syntheses in aqueous medium afforded moderate to excellent yield (up to 98%) within short reaction time and allowed the reaction to take place with low microwave power (200 W). This synthetic methodology provides easier separation of products and the catalyst exhibits recycling ability without loss of its catalytic activity up to five reaction cycles. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:267–271, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/hc.20197     

Synthesis of hantzsch 1,4‐dihydropyridines under solvent‐free condition using zn[(L)proline]2 as lewis acid catalyst

The present short communication describes a Lewis acid (Zn[(L)proline]₂) catalysed one pot synthesis of Hantzsch 1,4‐dihydropyridine (DHP) derivatives under solvent‐free condition by conventional heating and microwave irradiation. The Lewis acid catalyst Zn[(L)proline]₂ used in this reaction afford moderate to good yield. The catalyst is reusable upto five cycles without appreciable loss of its catalytic activity.     

Silica‐supported synthesis of some 1,3,5‐trisubstituted 2‐pyrazolines under solvent‐free and microwave irradiation conditions

A simple method for the synthesis of 2‐pyrazolines is described which occurs on silica surface under solvent‐free conditions within 110‐180 sec using microwave irradiation. The results obtained indicate that the use of silica gel as a support in pyrazoline formation reactions can have a profound effect on reaction rates and yields and cause cleaner reaction conditions.     

Scavenging activity of C4‐hydroxyphenyl‐ and polyhydroxyphenyl‐1,4‐dihydropyridines toward free radicals

The radical‐scavenging ability of synthesized C4‐phenolic‐substituted 1,4‐dihydropyridines (1,4‐DHPs) toward 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH^?) and alkyl/alkylperoxyl ABAP‐derived radicals at pH 7.4 was assessed by UV–visible spectroscopy. Reactivity of 1,4‐DHPs toward DPPH^? was measured by following the decay of the absorption corresponding to the radical λ_max at 525 nm, permitting the calculation of EC₅₀, t_EC50, and antiradical efficiency values. Pseudo–first‐order kinetic rate constants for the reactivity between the C4‐phenolic‐substituted 1,4‐DHP compounds and alkyl/alkylperoxyl ABAP‐derived radicals were followed by the decrease in λ_max at 356 nm corresponding to 1,4‐DHP moiety. C4‐phenolic‐substituted 1,4‐DHPs were more reactive toward alkyl free radicals than the other tested radicals. The 3,4,5‐trihydroxyphenyl‐1,4‐DHP was the most reactive derivative toward this radical with a kinetic rate constant value of 513.2 s^?1. Also, this derivative was the most effective toward the DPPH^? radical with the lowest EC₅₀ value (5.08 µM). Comparative studies revealed that synthesized 1,4‐DHPs were more reactive than commercial 1,4‐DHPs. The scavenging mechanism involves the contribution of both pharmacophores, that is, hydroxyphenyl and 1,4‐DHP rings, which was supported by the identification of the reaction products. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 44: 810–820, 2012     

Barium nitrate catalyzed one pot synthesis of 1,4‐dihydropyridines under solvent free conditions at room temperature

Barium nitrate acts as an efficient catalyst for the three‐component one pot synthesis of 1,4‐dihydropyridines. Barium nitrate is a safe chemical, and reaction without the use of organic solvents makes the process eco‐friendly.     

Claycop/hydrazine: A new and highly efficient recyclable/reusable catalytic system for 1,4‐disubstituted‐1,2,3‐triazole synthesis under solvent‐free conditions

Clay‐supported copper(II) nitrate (claycop) has been used as an efficient catalyst for azide–alkyne cycloaddition reactions leading to 1,4‐disubstituted 1,2,3‐triazoles. The highly efficient claycop/hydrazine hydrate catalytic system affords triazoles in a few minutes (1–20 min) at room temperature, under mild and solvent‐free conditions. High regioselectivity, excellent yields, ease of claycop synthesis and recyclability/reusability of the catalyst are considered as practical merits of the protocol.     

Synthesis of some 2‐oxo and 2‐thioxo substituted pyrimidines using solvent‐free conditions

A series of oxo‐ and thioxopyrimidines 4 ( a‐m ) were synthesized by one‐pot three components cyclocondensation reaction of β‐ketoester, aldehyde and urea/thiourea using benzyltriethylammonium chloride as a catalyst under solvent‐free conditions. The yields of products following recrystallization from ethanol were of the order of 65‐87%. IR and ¹HNMR spectroscopy and elemental analysis were used for identification of these compounds.     

Efficient synthesis of 5,10,15‐triarylcorroles using amberlyst 15 under solvent‐free conditions

An efficient and convenient synthesis of 5,10,15‐triarylcorroles by the condensation of aryl aldehydes with pyrrole catalyzed by Amberlyst 15 followed by oxidative cyclization with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) at room temperature has been reported. Amberlyst 15 is more efficient catalyst under solvent free conditions and DDQ is more suitable oxidant in dichloromethane than those of other catalysts and oxidants, respectively, for the synthesis of corroles at room temperature.     

Phenylphosphinic acid‐catalyzed synthesis of 6‐unsubstituted dihydropyrimidinones under solvent‐free conditions

Phenylphosphinic acid is found to catalyze the three‐component condensation of an aldehyde, enaminone, and urea or thiourea to afford the corresponding 6‐unsubstituted dihydropyrimidinones in high to excellent yields. This methodology is simple and fast synthetic route for the preparation of interesting class of heterocycles.     

An efficient one‐pot synthesis of 2‐aminopyrimidinomethylnaphtols under solvent‐free conditions

A novel one‐pot three‐component condensation reaction of an aldehyde, 2‐aminopyrimidine and 2‐naphthol to afford the corresponding 2‐aminopyrimidinomethylnaphtols in good yields. The remarkable features of this new procedure are high conversions, short reaction time, clean reaction profiles, and environmentally benign and simple work‐up procedures.     

Synthesis and chemistry of new spiro‐Δ1‐pyrazoline

In explorations of syntheses and chemistry of spiroheterocycles, we found that the reaction of 2‐diazopropane with (E)‐α‐arylidenepyrrolin‐2‐one, (E)‐α‐arylidene‐γ‐butyrolactone, and (E)‐arylidene‐N‐arylsuccinimide derivatives produced spiro‐Δ¹‐pyrazolines. The photolysis of Δ¹‐pyrazolines has led to cyclopropanes. The structures of the obtained adducts have been assigned by means of spectroscopic measurements. J. Heterocyclic Chem., (2011).     

A facile synthesis of 2,3-disubstituted-6-arylpyridines from enaminones using montmorillonite K10 as solid acid support

A facile synthesis of 2,3-disubstituted-6-arylpyridines from enaminones using montmorillonite K10 as solid acid support is reported herein.     

An efficient synthesis of 2,3‐dihydroquinazolin‐4(1H)‐one derivatives under catalyst‐free and solvent‐free conditions

A simple, efficient and convenient one‐pot synthesis of 2,3‐dihydroquinazolin‐4(1H)‐one derivatives under solvent‐free and catalyst‐free conditions by the reaction of aromatic aldehydes, isatoic anhydride, and ammonium acetate was reported. The advantages of this protocol include short reaction time, mild reaction conditions, easy work‐up, high yields, and environmental friendliness. J. Heterocyclic Chem., (2011).     

Tandem synthesis of 2,3‐dihydroquinazolin‐4(1H)‐ones on grinding under solvent‐free conditions

Citric acid promoted synthesis of a mini‐library 2,3‐dihydroquinazolin‐4(1H)‐ones with good to excellent yields is achieved by tandem reaction of anthranilamides (or anthranilhydrazides) with aldehydes on grinding at room temperature under solvent‐free conditions. This method has notable advantages in terms of simple workup, short reaction time, cost‐effective, and environmentally benign. J. Heterocyclic Chem., (2012).     

Comparative use of solvent‐free KF‐A12O3 and K2CO3 in acetone in the synthesis of quinoxaline 1,4‐dioxide derivatives designed as antimalarial drug candidates

In this paper we describe two new basic conditions for the synthesis of quinoxaline 1,4‐dioxide derivatives in moderate to good yields. These conditions, exemplified by the use of K₂C0₃ in acetone or KF/A1₂0₃ in the absence of an organic solvent, were reproducible and applicable to the synthesis of 2‐(carboethoxy)‐3‐phenylquinoxaline 1,4‐dioxide derivatives substituted in position 4 with electron‐donating or electron‐withdrawing groups.