Angelw reports a new "Jinbao" for the synthesis of complex polycyclic systems by activation of hydrocarbon bonds

It is a great challenge in organic synthesis to synthesize complex polycyclic compounds simply and efficiently from simple and easily available molecules, especially the almost ubiquitous hydrocarbons In recent ten years, due to the unique activity, selectivity and functional compatibility of cyclopentadienyl trivalent cobalt and rhodium catalysts for the activation of hydrocarbon bonds, they have been widely studied Recently, the research group of metal complexes and molecular activation of Dalian Institute of Chemical Physics, Chinese Academy of Sciences has made a series of progress in this field, and the relevant work has been published in the German Applied Chemistry (angelw Chem Int ed 2016, 55, 15351) and (angelw Chem Int ed doi: 10.1002/anie.201704036) Nitrones are usually used as classical 1,3-dipoles in various cycloaddition reactions In 2013, the team realized the activation of nitrone based hydrocarbon bonds for the first time However, it has not been reported that it can be used as aromatics substrate to realize the combination of hydrocarbon bond activation and dipolar addition Recently, the team used nitrone as the dipole positioning group, first through the activation of hydrocarbon bond and cyclopropene to realize acylation In situ, the activated C = C double bond and nitrone generated intramolecular 1,3-dipolar addition to obtain the bridge ring compound The reaction is suitable for N-tert-butyl and n-aryl-nitrone with larger steric hindrance For n-tert-butyl-nitrone, the hydrocarbon activation takes place in the only ortho position of benzene ring; for n-aryl-nitrone, the reaction takes place in N-aryl ring, so the structure of the product is different It is worth mentioning that for n-tert-butylnitrone, the reaction shows the selectivity of potential resistance control of nitrone substrate When the ortho substituent hindrance of n-tert-butylnitrone is small, although the reaction also undergoes C-H activation and the insertion and ring opening of p-ternary ring, the resulting alkenyl rhodium carbon bond is not proton resolved, but the insertion of electrophilic imine segment occurs, and then undergoes β - carbon atom elimination and proton decomposition, resulting in the final 1-naphthol product In the reaction, nitrone played the role of electrophilic traceless guiding group This part of the work was published on angew Chem Int ed 2016, 55, 15351 Because of the active terminal alkyne and α, β - unsaturated ketone structure, Cyclohexanedione containing alkyne fragments has many reaction possibilities, which has been one of the research hotspots all the time, but most of the researches are focused on the nucleophilic properties of the substrate It is the first report that the Diels alder reaction takes place by combining it with indole which is widely existed in natural products Firstly, the metal carbon bond was formed by activation of the hydrocarbon bond, then the alkyne was inserted in situ to form the diene intermediate, and then diel alder reaction occurred with the amphiphilic (Cyclohexanedione), in which the metal always participated The bridge ring and bicyclic compounds with different structures can be obtained When rhodium is used as catalyst, the common 2,1-insertion of rhodium carbon bond on alkynes is followed by the first type of D-A cyclization to obtain the parallel ring, and the rare 1,2-insertion and the second type of D-A cyclization to obtain the bridge ring with the rare structure when the smaller radius cobalt catalyst is used This work was recently published in German Applied Chemistry (angel Chem Int ed doi: 10.1002 / anie 201704036) Paper link: http://onlinelibrary.willey.com/doi/10.1002/anie.201704036/full