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Study On The Hypervalent Iodine Reagent-mediated Synthesis Of [1,2,4]-Triazolo-[1,5-a]pyridine And Acridone Derivatives

Posted on:2015-12-27Degree:DoctorType:Dissertation
Country:ChinaCandidate:Z S ZhengFull Text:PDF
GTID:1221330452970610Subject:Applied Chemistry
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[1,2,4]-Triazolo-[1,5-a]pyridine derivatives and acridone derivatives are importantheterocyclic compounds with significant biological and pharmaceutical activities,which were introduced in Chapter one together with their synthetic strategies. Asfurther understanding of their applications and rapid development of newlydiscovered structures, efficient and convenient methods for the synthesis of thoseheterocycles are highly demanded, to meet the need of development of modernmedicine. Therefore, two novel synthetic strategies to [1,2,4]-triazolo-[1,5-a]pyridinederivatives and acridone derivatives mediated by hypervalent iodine reagents weredeveloped and introduced in Chapter Two and Three, respectively.In Chapter Two, we described the PIFA-mediated novel synthesis of[1,2,4]-triazolo-[1,5-a]pyridines via intramolecular oxidative cyclization of variousN-(pyridin-2-yl)-imidamides. Meanwhile, a possible mechanism for this oxidativetransformation was proposed based on the experimental data during the reactioncondition screening and the preparation of the [1,2,4]-triazolo-[1,5-a]pyridines, that is,the reaction might proceed via the N-iodoimido intermediate (or N-iodoenaminospecies), which then cyclized to form the nitrenium intermediate, followed byrearomatization。 This intramolecular metal-free strategy to the construction of[1,2,4]-triazolo-[1,5-a]-pyridines via a N-N bond formation features short reactiontime, mild condition, high yields, and simple workup, which also greatly expands theapplications of hypervalent iodine reagent in construting heterocyclic compounds viaintramolecular N-N bond formation.In Chapter Three, we described the PIDA-mediated novel synthesis of acridonederivatives via intramolecular oxidative aryl-aldehyde Csp2-Csp2bond formation.Meanwhile, a possible mechanism for this cross-dehydrogenative coupling (CDC)was also proposed, that is, initiation of BPO under heat generated free radical, whichreacted with PIDA to form the hypervalent iodine radical species. The iodine radicalintermediate would abstract the hydrogen radical from aldehyde substrate to affordacyl radical, which then cyclized to give cyclohexadienyl radical. Finally, the cyclohexadienyl radical would lose a hydrogen radical to afford the acridonederivative directly. Alternatively, it would produce the cyclized product via a SETprocess, followed by rearomatization. This intramolecular metal-free strategy to theconstruction of acridone derivatives was also the first report on the combination ofiodine (III) reagent and radical initiator (BPO) promoting the oxidative C-C bondformation.
Keywords/Search Tags:hypervalent iodine reagent, N-N bond formation, cross-dehydrogenative coupling, radical, Csp2-Csp2bond formation, intramolecularoxidative cyclization
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