Study On Synthesis Of 3-nitrosoindole Derivatives Through Rh-Catalyzed C(sp~2)-H Bond Activation And DG Transfer

Transition-metal-catalyzed direct C-H bond activation(CHA)has become an important organic synthetic strategy in the term of high step-and atom-economical In this regime,a directing group(DG)not only enhance reactivity,but also solve the problem of regioselectivity in organic molecules containing multiple C-H bonds Nevertheless,they always bring chemical traces in the products,which limits the structural diversity.For the sake of overcoming the disadvantage,we pioneered a traceless N-O oxidizing DG,in which the N-O group play the dual role of DG and internal oxidant,and allowed convenient removal after the C-H functionalization.The research has attracted the attention of international peers,which has developed various internal oxidative DG such as O-O,N-O and N-N groups.Incorporation of the DG into a product via CHA/DG migration is an alternative strategy to not only realize a highly atom-economical process and reuse of the DG,but also promotes the development of multitasking DGs.On the other hand,indoles are crucial heterocyclic compounds found in pharmaceutical and chemical fields.Although the traditional Fischer indole synthesis has remained one of the most widely employed methods,there are some problems,including complicated steps,low atom-economy and harsh reaction conditions.Base on this,we took the strategy,which involves CHA and DG migration to develop a novel method to synthesize indoles by using cheap and readily available raw materials as substrates.The main results obtained are as follows:Rh(?)-Catalyzed Tandem C-H Acylmethylation,Nitroso Migration and Cyclization:Approach to 3-Nitrosoindoles3-Nitrosoindoles were employed as important intermediates in organic synthesis for the preparation of various LED polymers and high-spin organic polymers.We have developed a novel protocol for the synthesis of 3-nitrosoindoles.The readily available N-nitrosoanilines and benzoyl sulfoxonium ylides are used as substrates Rh(?)-Catalyzed tandem acylmethylation and trifluoroacetic acid(TFA)mediated nitroso transfer and cyclization are involved in one pot manners(Scheme 1).The N-nitroso group acts as both DG and nitrosation agent.One C-C bond and two C-N bonds were formed.This process tolerated broad substrates with high atom-economy and regioselectivity and avoided the external oxidants.In addition,the further chemical conversion of the product enhances the synthetic value of the method.According to the related literature and experimental results,a plausible mechanistic pathway is proposed(Scheme 2).