Ultrasonic Cavitation Facilitates Rapid Synthesis of Trisubstituted Pyrazole Scaffolds through Michael Addition/Domino Cyclization

Abstract

A series of aryl/indolyl substituted 4, 5‐dihydro‐1H‐pyrazole derivatives were synthesized via a domino method based on Michael addition mediated cyclization of appropriate chalcones. The chalcones were prepared by Witting reaction in which substituted aromatic aldehydes were treated with stable ylides under eco‐friendly ultrasonic cavitation. The pyrazole scaffolds were obtained in excellent yields within a short span of time.

Synthesis of pyrimido[4,5- b ]quinolindiones and formylation: ultrasonically assisted reactions

“…A chloromethyleneiminium salt, with a known formation mechanism, was prepared using this process [33]. For the formylation of methylene groups under VH conditions, the reaction is typically promoted by heating, and reports have shown that the reactions can be accelerated by microwave and ultrasound radiation [41][42][43][44]. In our work, to obtain β-chlorovinyl aldehyde derivatives 6 and 7, the reaction was not explored under reflux or controlled temperature heating conditions, and ultrasound-assisted conditions allowed the control of HCl release.…”

The green chemistry of chalcones: Valuable sources of privileged core structures for drug discovery

“…Chalcones exposed to aryl hydrazides undergo a Michael addition-cyclization reaction, forming the corresponding pyrazole scaffolds. This reaction was carried out both by conventional method and ultrasonic irradiation, the latter allowed to decrease the reaction time with a comparable yield ( Kannan et al, 2019 ). Thanks to the success of the previous reaction, Kannan and co-workers extended the synthetic process to indole-based chalcones by reacting them with different carbohydrazides following the same ultrasonication conditions reported above ( Kannan et al, 2019 ).…”

“…This reaction was carried out both by conventional method and ultrasonic irradiation, the latter allowed to decrease the reaction time with a comparable yield ( Kannan et al, 2019 ). Thanks to the success of the previous reaction, Kannan and co-workers extended the synthetic process to indole-based chalcones by reacting them with different carbohydrazides following the same ultrasonication conditions reported above ( Kannan et al, 2019 ). Finally, a one-pot cyclo condensation reaction was performed between chalcone derivatives and o -aminothiophenol by Devkate et al In their approach, several solvents were tested and PEG-400 was identified as the best choice providing a shorter reaction time and straightforward separation procedures for the target 1,5-benzothiazepines ( Devkate et al, 2018 ).…”