Advances in the last decade for the synthesis of the imidazo[1,2-a]pyridine scaffold from various substrates employing approaches such as multicomponent reactions, tandem processes, rearrangement reactions, inter- and intramolecular oxidative/reductive cyclizations, and transition-metal-catalyzed C–H activation are summarized in this review. The mechanisms for the selected transformations are also discussed. 1 Introduction 2 From 2-Aminopyridines 2.1 Revisiting Traditional Cyclocondensation 2.1.1 Regioselectivity in Cyclocondensation 2.2 Reactions of Carbonyl Compounds 2.3 Reactions of α,β-Unsaturated Carbonyl Compounds 2.4 Reactions of Nitroolefins 2.5 Reactions of Alkynes 2.6 Multicomponent Reactions 2.6.1 Three-Component Reaction of Aldehyde, 2-Aminopyridine, and Isocyanide 2.6.2 Three-Component Reaction of 2-Aminopyridine, Aldehyde, and Alkyne 2.6.3 Other Multicomponent Procedures 2.7 Reactions of N-Substituted 2-Aminopyridines 2.8 Miscellaneous Reactions 3 From Pyridines 3.1 Multicomponent Reactions 4 From Pyridinium Salts 5 From Imidazoles 5.1 Reactions of Heterocyclic Ketene Aminals 6 Miscellaneous Methods 7 Conclusion

1-aminocyclopropane-1-carboxylate deaminase (ACCD), a pyridoxal phosphate dependent enzyme, is widespread in diverse bacterial and fungal species. Owing to ACCD activity, certain plant associated bacteria help plant to grow under biotic and abiotic stresses by decreasing level of 'stress ethylene' which is inhibitory to plant growth. ACCD breaks down ACC, an immediate precursor of ethylene, to ammonia and α-ketobutyrate which can be further metabolized by bacteria for their growth. ACC deaminase is an inducible enzyme whose synthesis is induced in presence of its substrate ACC. This enzyme, encoded by gene AcdS, is under tight regulation and regulated differentilly under different environmental conditions. Regulatory elements of gene AcdS are comprised of regulatory gene encoding LRP protein and other regulator elements which are activated differentially under aerobic and anaerobic conditions. Role of some additional regulatory genes such as AcdB or LysR may also be required for expression of AcdS. Phylogenetic analysis of AcdS has revealed that distribution of this gene among different bacteria might have resulted from vertical gene transfer with occasional horizontal gene transfer. Application of bacterial AcdS gene has been extended by developing transgenic plants with ACCD gene which showed increased tolerance to biotic and abiotic stresses in plants. Moreover, distribution of ACCD gene or its homologs in wide range of species belonging to all three domains indicate alternative role of ACCD in physiology of an organism. Therefore, this review is an attempt to explore current knowledge of bacterial ACC deaminase mediated physiological effects in plants, mode of enzyme action, genetics, and distribution in different species and ecological role of ACCD and, future research avenues to develop transgenic plants expressing foreign AcdS gene to cope with biotic and abiotic stressors. Systemic identification of regulatory circuits would be highly valuable to express the

An efficient procedure for catalyst solubility, recycling and easy product isolation in oxidation of thiols to disulfides with molecular oxygen catalyzed by cobalt(II) phthalocyanines dissolved in ionic liquid at room temperature is reported.