Shyam L. Gupta

An efficient ultrasound-assisted one-pot chemoselective synthesis of pyrazolo[3,4-b] pyridine-5-carbonitriles in aqueous medium using NaCl as a catalyst

A simple, convenient and green synthetic protocol for the chemoselective synthesis of pyrazolo[3,4-b]pyridine derivatives via three-component reaction of 3-amino-5-methylpyrazole, ethyl cyanoacetate, and aldehydes catalyzed by sodium chloride under ultrasound irradiation in aqueous medium is described. The method showed remarkable selectivity for pyrazolo[3,4-b]pyridine over dehydrogenated pyrazolopyridines, bis-pyrazolopyridines and pyrazolo[1,5-a]pyrimidine derivatives. The reactions were carried out under both conventional and ultrasonic irradiation conditions. Under ultrasound radiation, the catalytic activity of NaCl was about 15-fold higher as compared to the conventional method. The sonochemical procedure offers several advantages including cleaner reaction profile, use of easily available, cheap and environmentally benign catalyst, high yields, and simple experimental and work-up procedures.

Ultrasound-assisted facile and selective synthesis of azeto[2,1-d][1,5]benzothiazepines under solvent-free conditions and their biological activity

A facile, efficient and environmentally friendly heteroannulation protocol for the exclusive synthesis of medicinally important azeto[2,1-d][1,5]benzothiazepines 3 has been developed in the presence of 10 mol% K2CO3 under sonication. In comparison to conventional synthesis, where mixture of products such as 3, phenyl-N-acetyl-2-styrylbenzothiazole 4 and 1,3-oxazine derivative 5 were formed in several hours of heating, the present method provides several advantages including selective synthesis of 3 with simpler work-up procedure, higher yields in shorter reaction time and green aspects through the avoidance of toxic catalysts and solvents.

Molecular Iodine: Mild, Green, and Nontoxic Lewis Acid Catalyst for the Synthesis of Heterocyclic Compounds

The synthetic uses of molecular iodine are described. This chapter discusses the versatile uses of iodine in heterocyclic synthesis. Iodine is a universal oxidizing agent, a mild and nontoxic Lewis acid catalyst, and it catalyzes various organic reactions with high efficiency and selectivity. Also, iodine acts as an electrophile–nucleophile dual activator in the reactions. Further applications are the introduction of protecting groups, deprotection, iodocyclization, C–C bond formation, and formation of heterocycles. It is quite clear from the growing number of emerging publications in this field that the possibility to utilize this technology allows accessing the reaction conditions that is valuable for heterocyclic synthesis. The present chapter focuses on literature reports for the period of 2003–2013.

Recent Advancements of Copper as an Inexpensive and Mild Catalyst in Heterocyclic Synthesis

Recent studies showed that Cu-catalysts proved to be a boon for heterocyclic synthesis. The Cu-catalysts made oxidative cross-coupling reaction s, hydrogen transfer, carbon-carbon, carbonheteroatom and heteroatom-heteroatom bond formation s. It is environmentally benign and inexpensive than other transition-metal catalysts in organic sy nthesis. This review summarizes the recent advancements in Cu (I), Cu (II), and Copper nanopar ticles catalyzed coupling reactions and synthesis o f various complex heterocyclic compounds in mild cond itions.