Ultrasound-promoted Synthesis Of Heteroaromatic N-oxides And 2-sulfonyl Quinolines

Green chemistry is a new concept proposed in twenty-first century,which is a"new chemical baby".In an era of serious climate changes,humanity will be forced to strengthen endeavors in the direction of sustainable development.Green chemistry has become an important subject in organic chemistry.Reducing the use of hazardous reagents and solvents,minimizing the production of harmful waste,and enhancing safety,cost-and atom efficiency,with renewa’ble resources in operationally simple processes are the prime targets in this regard.Ultrasound-assisted organic synthesis is the most important component in green organic synthesis.Compared to conventional thermal heating,ultrasound irradiation has some important advantages:ultrasonification largely enhances the reaction rate and reduces the reaction times,improves yields,minimizes side product formation by providing the activation energy in micro environment,easier manipulation,increased selectivity,using small amounts of solvents,mild reaction condition and offers environmentally friendly and sustainable synthetic processes.This thesis is concerned on the ultrasound assisted oxidation and ultrasound assisted sulfonylation.It is divided into three parts as follows:1.Heteroaromatic N-oxides are important heterocyclic compounds,acting as versatile building blocks and synthetic intermediates in organic synthesis.The heteroaromatic N-oxides structure presents prevalently in natural products,pharmaceuticals and biologically relevant lead compounds as a key fragment.A convenient and efficient protocol for the ultrasound assisted synthesis of heteroaromatic N-oxides through Nafion-H catalyzed oxidation of nitrogen heterocycle with H2O2 was developed.We have examined the impact of the resin cations,bases,solvents,ultrasonic power and frequency respectively by establishing a model reaction using quinoline as the substrate,and obtained the optimum reaction conditions.The advantages of this protocol include easily recoverable catalyst,a wide range of substrates,mild reaction conditions,good to excellent yields practical convenience,and readily available starting materials.2.2-Sulfonylqui oline and its related derivatives are important structural units those have received considerable attention in synthetic chemistry,mainly because they constitute a significant component in biologically active compounds and also serve as useful chemical intermediates for synthesis.A convenient and efficient protocol for the ultrasound assisted synthesis of 2-sulfonyl quinolines/pyridines directly from heteroaromatic N-oxides and sulfonyl hydrazides using chlorotripyrrolidinophosphonium hexafluorophosphate as an activating reagent without transition metal catalyst or oxidant was developed.We have examined the impact of the activating agents,bases,solvents,ultrasonic power and frequency respectively by establishing a model reaction using quinoline-N-oxide and tosylhydrazine as the substrates,and obtained the optimum reaction conditions The advantages of this protocol include a wide range of substrates,mild reaction conditions,good to excellent yields practical convenience,and readily available starting materials.