Iodine-containing Compounds Mediated Oxidative Cyclization And C-N Bond Formation Reactions

In recent years, iodine-containing compounds have attracted sustained attention for their broad applications in organic synthesis. Iodine-containing compounds mediated reactions are nowadays not only for the classic oxidation of alcohols and iodination reactions, but also for oxidative cyclization, asymmetric synthesis, the construction of carbon-heteroatom bonds and heteroatom-heteroatom bonds. Therefore, iodine-containing compounds have become a kind of practical reagents in organic synthesis. However, some researches also need to be done in this field, such as, carbon-carbon bond formation for the synthesis of carbocycles, oxidative amination of chain C(sp2)-H bonds, improvement of atom economy of the reactions, and development of green, efficient reaction systems.Herein, on the basis of unique nature of iodine-containing compounds, the utilization of iodine-containing compounds for C-N bond formation and oxidative cyclaztion were investigated. Seven reaction systems were developed, including electrophilic cyclization reactions, radical reactions, degradation reactions and so on. To our knowledge, using tri-valent hyperidine regeants in the areas like naphthalene amino esters synthesis through intermolecular construction of two C-C bonds and synthesis a-amino-β-enamine compounds through C(sp2)-H oxdative amination strategies has no report till now. The work of this paper give a better understanding of the properties of iodine-containing compounds and may provide a basis for expanding the application of iodine-containing compounds.An intermolecular two C-C bond formation procedure for the synthesis of carbocycles mediated by hypervalent iodine(III) reagents was developed.This metal free protocol provided a new approach for the synthesis of useful substituted naphthalene amino esters via benzannulation reactions. Various of N-non substituted and N-alkyl substituted aromatic enamines with terminal alkynes and non-terminal alkynes can be converted into corresponding naphthalene amino esters with yield up to91%. Good functional group tolerance, readily available material and high atom utilization efficiency make this method more practical. After a series of control experiments, it was confirmed that the products were obtained via an oxidative cascade procedure and alkynes and aromatic rings behaved as nucleophiles respectively.Phenyliodine diacetate was found as a powerful reagent for the desulfidation and degradation of1,3-disubstituted thiourea to acetanilides, yields ranging from80-93%. Temperature and base were the key roles of the reaction and carbodiimides, N-acetylureas, or acetanilides could be obtained in different temperatures.Enamine compounds were efficiently aminated via an C(sp2)-H activation procedure mediated by PhI(NTs2)OAc, which was both the oxidant and the amination reagent. α-Amino-β-enamine compounds could be obtained under mild conditions with good yields. Good functional group tolerance, readily available material and high atom utilization efficiency make this method more practical.Two methods were developed for the synthesis of dibenzopyranones from2-arylbenzoic acids using PhIO and NIS as oxidant respectively. Reactive electrophilic intermediates were generated in the procedure of PhIO mediated oxidative cyclization of2-arylbenzoic acids to dibenzopyranones, which was the key step in the reaction. A series of dibenzopyranones could be synthesized under the mild condtions with yield up to81%. N-iodosuccinimide was found as a efficient oxidant for this transformation, too. The methodology is distinguished by its practicality in terms of its wide substrate scope, good functional group tolerance, and mild reaction conditions without the use of transition metals. Furthermore, the reaction was also scaled up to a gram scale and applied for the synthesis of complex compounds, and both good results were obtained.Bu4NI and tBuOI were used for the synthesis of2,5-disubstituted1,3,4-oxadiazoles respectively. Hydrazides could directly convert to2,5-disubstituted1,3,4-oxadiazoles catalyzed by Bu4NI using TBHP as oxidant under mild conditions. Oxidative cyclization of N-acylhydrazones to2,5-disubstituted1,3,4-oxadiazoles also could be achieved. Heterocyclic and alkyl hydrazides reacted well under the optimized conditions, which made the substrate scope extremely broad. An efficient procedure for the oxidative cyclization of N-acylhydrazones was developed utilizing tBuOI, which is generated in situ from tBuOCl and NaI. A variety of2,5-disubstituted1,3,4-oxadiazoles were synthesized in yield ranging from75%to95%within short reaction time. The method is also suitable for cyclization of N-acylhydrazones derived from heterocyclic aldehydes and aliphatic aldehydes.