Facile Synthesis of Pyrano[2,3‐c]pyrazol‐6‐one Derivatives Under Microwave Irradiation in Solvent‐Free Conditions

A series of substituted 1H,6H‐pyrano[2,3‐c]pyrazol‐6‐one derivatives were synthesized from one‐pot cyclocondensation of hydrazine derivatives or 1H‐pyrazol‐5‐one derivatives with various β‐keto esters under solvent‐free conditions using microwave irradiation in short time with good to excellent yields.     

One‐Pot Preparation of Fluorinated α‐Aminoalkyl Phosphonates under Microwave Irradiation and Solvent‐Free Conditions

A facile one‐pot method has been developed for the synthesis of fluorine‐containing α‐amino phosphonates in good yields by a three‐component reaction of fluorinated aromatic aldehydes, anilines, and diethyl phosphate in the presence of a silica‐gel support under microwave irradiation within 10 min. All new compounds are fully characterized by spectral methods and elemental analysis.     

One‐Pot Synthesis of Iminoimidazolines under Microwave Irradiation in Solvent‐Free Conditions

Substituted iminoimidazolines were synthesized from a one‐pot reaction of aromatic or hetero‐aromatic amines with imidazolidine‐2‐thione under solvent‐free conditions using microwave irradiation with good to excellent yields.     

Synthesis of 2‐Substituted 4,5‐Diphenyloxazoles under Solvent‐Free Microwave Irradiation Conditions

A novel method for the direct conversion of deoxybenzoin into 2‐alkyl‐4,5‐diphenyloxazoles and 2‐aryl‐4,5‐diphenyloxazoles has been developed using treatment of HTIB and nitriles under solvent‐free microwave irradiation conditions.     

Microwave‐Enhanced Ferrier Reaction: A Facile Synthesis of 2,3‐Unsaturated‐O‐Glycosides Under Solvent‐Free Conditions

A variety of 2,3‐unsaturated‐O‐glycosides have been prepared by the Ferrier rearrangement of acetyl protected glycals under microwave irradiation using silica gel as an acid catalyst. Environmental friendliness, high yields, and short reaction times are the key features of this method. Furthermore, the method was applicable not only to the Ferrier reaction of 3,4,6‐tri‐O‐acetyl glucal and 3,4,6‐tri‐O‐acetyl galactal but also to the Ferrier reaction of 3,4‐di‐O‐acetyl arabinal.     

Facile Deprotection of Aromatic tert‐Butyl and Allylic Esters Under Microwave Irradiation Conditions

Abstract

A simple and efficient method for the deprotection of tert‐butyl and allylic esters is described, which occurs under microwave irradiation with p‐toluenesulfonic acid in solvent‐free conditions.     

Lithium Perchlorate Mediated Three‐Component Preparation of α‐Aminonitriles Under Solvent‐Free Conditions

Abstract

A three‐component reaction between aliphatic or aromatic aldehyde, an amine and trimethylsilyl cyanide mediated by solid LiClO₄, gave amino nitriles in good to excellent yields. The reaction proceeded smoothly under solvent‐free conditions without any side products.     

Microwave‐Assisted Ring Opening of Epoxides in Solvent‐Free Conditions

The reaction of aryloxymethyl epoxide with anilines under solvent‐free conditions and microwave irradiation affords high yields of 1‐arylamino‐3‐aryloxypropan‐2‐ols. The reaction was rapid and completely regioselective.     

Microwave‐Assisted One‐Pot Preparation of Tetrahydro‐β‐carboline Hydrochlorides under Solvent‐Free Conditions

An efficient and environmentally friendly synthesis of tetrahydro‐β‐carboline hydrochlorides via Pictet–Spengler reaction was described. Tryptamine hydrochlorides were used as the reactant and no additional acid catalyst was needed. This reaction was completed within 2.5–9 min in good yield.     

Microwave‐Assisted Protection of Phenols as tert‐Butyldimethylsilyl (TBDMS) Ethers Under Solvent‐Free Conditions

Abstract

A facile, time‐saving procedure to protect phenols with tert‐butyldimethylsilyl chloride using imidazole as catalyst under solvent‐free conditions is described. Several phenolic compounds with different substitution patterns can be silylated in high yield with substantially reduced generation of residues, a present goal in organic synthesis.     

Porous Calcium Hydroxyapatite as an Efficient Catalyst for Synthesis of Pyrazolines via 1,3‐Dipolar Cycoloaddition Under Solvent‐Free Microwave Irradiation

Adsorbed on porous calcium hydroxyapatite, 1,3‐dipolar cycloaddition of diphenylnitrilimine on olefins is readily catalyzed under solvent‐free microwaves irradiation. The pyrazolines are obtained in few minutes with high yields. Specific surface of porous calcium hydroxyapatite and microwaves effects are discussed.     

Efficient Synthesis of Phosphono‐ and Phosphinoxidomethylated N‐Heterocycles under Solvent‐Free Microwave Conditions

Simple N‐heterocycles were converted to N‐phosphono‐ and phosphinoxidomethyl derivatives by a solvent‐free microwave‐assisted condensation of the heterocycle, paraformaldehyde, and diethylphosphite or diphenylphosphine oxide in a convenient and, in most cases, efficient way. In contrast to an earlier report, imidazole proved to be unreactive in this type of phospha‐Mannich reaction.     

Regioselective Aromatic Electrophilic Bromination with Dioxane Dibromide Under Solvent‐Free Conditions

Highly regioselective ring bromination of aromatic compounds has been accomplished with high yields and good purity using dioxane dibromide (DD) under solvent‐free conditions. Notable features of this methodology include operational simplicity, rapid reactions, excellent control over the degree of bromination, and tolerance of various functional groups during the reaction.     

Microwave‐Assisted Synthesis of Amide under Solvent‐free Conditions

An efficient and environmentally friendly synthetic method for the synthesis of primary amides under microwave irradiation was described, in which the primary amine was directly reacted with acid without any catalytic agents. The reaction took place in 8–12 min, which was much shorter than the traditional synthetic methods, with almost quantitative yields. The influential factor of the reaction was discussed. The tautomerization between the carboxylic acid group and the H atom in α‐carbon of L‐amino acid was observed, presumably a dehydrated intermediate forming from this tautomerized isomer.     

PEG‐SO3H as Catalyst for 3,4‐Dihydropyrimidones via Biginelli Reaction Under Microwave and Solvent‐Free Conditions

An efficient and environmentally friendly process for the synthesis of 3,4‐dihydropyrimidones via the Biginelli‐type condensation reaction using poly(ethylene glycol)‐bound sulfonic acid as catalyst irradiated by microwave has been developed. The functionalized poly(ethylene glycol) acted simultaneously as catalyst and as solvent in the condensation. The workup was easy, and the products were obtained in good to excellent yields and high purities.     

Synthesis of Substituted 1,4‐Dihydropyridines in Water Using Phase‐Transfer Catalyst Under Microwave Irradiation

Abstract

The synthesis of various substituted 1,4‐dihydropyridines has been achieved by the reaction of aldehydes, ethyl/methyl acetoacetates, and ammonium acetate in water using phase‐transfer catalyst under microwave irradiation. Compared to the classical Hantzsch's reaction conditions, this new method consistently has the advantage of good yields and short reaction times. Bifunctional compounds containing two units have been synthesized using dialdehyde as precursor in good yields.     

Microwave‐Assisted Efficient Synthesis of Dihydropyrimidines in Solvent‐Free Condition

Abstract

An efficient synthesis of 3,4‐dihydropyrimidinones from an aldehyde, a ketoester, and a urea or thiourea using a catalytic amount of ferric chloride hexahydrate is described. Microwave irradiation has been used to accelerate the synthesis of the Biginelli compounds under solvent‐free conditions and in a short reaction time and with good yield.     

Microwave‐Induced Conversion of Acid Hydrazides to N,N′‐Diacylhydrazines in Solvent‐Free Conditions

A new and efficient method of converting acid hydrazides 1 to the corresponding N,N′‐diacylhydrazines 2 under microwave irradiation and in solvent‐free conditions has been described.     

Efficient Synthesis of tert‐Butyl Ethers under Solvent‐Free Conditions

A simple and efficient synthesis of tert‐butyl ethers from various alcohols and substituted phenols using tert‐butyl bromide in the presence of basic lead carbonate as a catalyst. The catalyst is easily recovered via filtration and can be reused up to three times without appreciable loss of activity.     

Facile Synthesis of 5‐Benzylidene Rhodamine Derivatives under Microwave Irradiation

A series of 5‐benzylidenerhodamine derivatives were synthesized by the cross‐aldol condensation of an aromatic aldehyde with rhodamine or rhodamine acetic acid in sodium acetate/acetic acid under microwave irradiation. The reaction was completed in 8–20 min with 63–94% yields and was environmentally benign with easy workup.