A Study On Rhodium-catalyzed C-H Functionalization Using Azo As Directing Group

The synthetic methods for constructing C-C, C-N, C-O and otherbonds by C-H activation has attracted chemists’ attention andbecame an important research field. Rhodium(lll) complex has beenwidely researched as an important transition-metal-catalyst, becauseit has high activity, mild reaction conditions, good selectivity andthermal stability. Many significant achievements have achieved in thefield of rhodium-catalyzed C-H activation. In this paper, we haveexplored rhodium-catalyzed direct C-H functionalization ofazobenzenes with different reagents using azo as ditecting group,which further expand the use of rhodium catalyst in the application ofC-H activation.This paper includes the following three parts;Part1IntroductionThe recent progress of transition-metal-catalyzed C-H aminationand C-H cyanation reaction was reviewed in this chapter.Part2Rhodium (lll)-Catalyzed Direct C-H Amidation of Azobenzenes In this chapter，we have disclosed a rhoclium(lll)-catalyzecl directortho-amidation of azobenzenes with sulfonyl azides as the aminosource. The effect of catalyst，solvent, additive, base, the ratio ofreaction substrates and temperature on reaction activity werestudied in detail. The scope of reaction substrates was furtherexplored under optimized conditions. This reaction exhibits a broadsubstrate scope, high functional group tolerance, providing a varietyof sterically hindered ortho-substituted azobenzene derivatives ingood to excellent yield. At the sametime, we found that therich-electronic azobenzene derivatives more easily took place the C-Hamidation reaction and ortho-substituted substrates also gave goodyield. In addition, the C-H amidation of asymmetric azobenzene withp-toluenesulfonyl azide show good regioselectivity.Part3Rhodium (lll)-Catalyzecl Direct C-H Cyanation of AzobenzenesIn this chapetr， a rhod i u m-cata ly zed azo-group-directedortho-cyanation of symmetrical azobenzenes is described employingN-cyano-N-phenyl-p-toluenesulfonamide (NCTS) as a new organiccyano source. NCTS is a low toxicity and environmentally friendlycyanide and has received more attention as an electrophilic cyanatingreagent. We have screened the effect of catalyst, solvent，additive,base, the ratio of reaction substrates and temperature on reactionactivity to obtain optimal reaction conditions. By studying C-H cyanation of a series of azobenzene derivatives, we found that thereaction activity was obviously affected by electronic effect andsterically hindered of substituents. The results indicated that thedirect cyanation of aromatic azo compounds possessingelectron-donating groups was more effective than those withelectron-withdrawing groups. We also found that the reactionprovides lower products due to the sterically hindered effect fromsubstituents at the ortho-position of azobenzene. The presentprotocol tolerates many useful functional groups and provides a newmethod for synthesizing azobenzene derivatives with a cyano group.