Microwave-assisted, sequential four-component synthesis of polysubstituted 5,6-dihydroquinazolinones from acyclic precursors and a mild, halogenation-initiated method for their aromatization under focused microwave irradiation

Montmorillonite Clay-Promoted, Solvent-Free Cross-Aldol Condensations under Focused Microwave Irradiation

“…The need for this research became apparent in the course of our program on the use of aryl and heteroaryl trans-chalcones in heterocyclic synthesis [35][36][37][38], when we noticed the shortcomings of the currently available protocols for the synthesis of the required starting materials. Thus, we present here our studies on a solvent-free protocol for their synthesis under microwave irradiation conditions in the presence of a montmorillonite clay catalyst, its application to a large number of examples in order to establish its scope and a brief study of its subsequent generalization to other types of substrates.…”

Microwave-assisted multicomponent reactions in heterocyclic chemistry and mechanistic aspects

“…Quiroga and co-workers [123] envisioned an environmentally benign three-component microwaveassisted synthesis of pyrazolo [3,4-b]pyridine-5-spirocycloalkanedione 139 derivatives via a reaction between 5-(4-R-benzyl amino)pyrazoles 137, cyclic 1,3-diketones 6 and formaldehyde (138) in ethanol as solvent. The protocol shows good functional group tolerance with both EDG and EWG on pyrazoles resulting in moderate to good yields (Scheme 53).…”

“…Menéndez and co-workers [138] described an efficient microwave-assisted sequential four-component reaction of chalcones 157, acyclic 1,3-diketone 54, butylamine (158) and ammonium formate (159) using CAN as a catalyst and ethanol as solvent. This is followed by sequential addition of formamide (160) under microwave irradiation to yield polysubstituted 5,6-dihydroquinazolinones 161 in good to moderate yields (Scheme 64).…”

Ethyl 4,4''-Dibromo-5'-(butylamino)-2',6'-dinitro-[1,1':3',1''-terphenyl]-4'-carboxylate

“…The synthesis of our target compound started from precursor 1, which was in turn obtained in 77% overall yield by a microwave-assisted three-component reaction between butylamine, ethyl 3-oxobutanoate, and 4,4'-dibromochalcone [14], followed by dehydrogenation with DDQ in toluene [15,16]. Compound 1 was regioselectively nitrated in its central benzene ring in almost quantitative yield by treatment with sulfonitric mixture in acetic acid at 0 °C, followed by heating at 50 °C for 40 minutes (Scheme 1).…”