Development of some new protocols for expedient synthesis of diverse heterocyclic and carbocyclic scaffolds

Abstract

The central theme of this dissertation is to develop new protocols for expedient synthesis newlineof diverse heterocyclic and carbocyclic scaffolds. The work presented in this thesis has newlinebeen divided into five chapters: newlineChapter 1: Conjugated Small Organic Molecules: Synthesis and Characterization of 4- newlineArylpyrazole-decorated Dibenzothiophenes newline4-Arylpyrazole-decorated dibenzothiophenes have been synthesized. The synthesis newlineinvolves the treatment of 2,8-dibromodibenzothiophene with pyrazole under Ullmann-type newlineamination conditions for the dual C N bond formation. The selective bromination of the newlineresulting dual C N bonded 2,8-dipyrazolyldibenzothiophene, and the subsequent Suzuki newlineMiyaura reaction furnished the target conjugated materials comprising small organic newlinemolecules (Scheme 1). The electron-deficient dibenzothiophene-S,S-dioxide core was newlineobtained in quantitative yield. UV-Vis absorption studies indicated changes in the positions newlineof the peak maxima upon increasing the conjugation length. Electrochemical and newlinetheoretical investigations of selected synthesized materials are also included. newlineChapter 2: SOCl2and#8209;Catalyzed Meyerand#8722;Schuster Rearrangement of 3°-Propargylic Alcohols: newlineSynthesis of Densely Arene-Substituted Pyrazolines Bearing a Tetrasubstituted Carbon newlineCenter from and#945;,and#946;-Unsaturated Carbonyl Compounds and Arylhydrazines newlineMeyerand#8722;Schuster rearrangement of 3°-propargyl alcohol to the corresponding and#945;,and#946;- newlineunsaturated carbonyl compounds under SOCl2 catalysis has been reported. Terminal and newlineinternal propargyl alcohols efficiently participated in the reaction. Furthermore, we have newlinedemonstrated the synthetic utility of conjugated carbonyl compounds to access densely newlinearene-substituted pyrazolines bearing tetrasubstituted carbon center by reacting with arylhydrazine hydrochloride (Scheme 2). Isotopic labeling studies were carried out to gain newlineinsights into the reaction mechanism.Chapter 3: K2CO3-Mediated Intramolecular Oxa-Michael Cyclization of and#945;,and#946; Unsaturated newlineKetoximes: Synthesis of Densely Arene-Substituted