Synthesis of 2‐alkenylidene‐3‐oxoindolines: cascade reactions of 4H‐furo [3,2‐b]indoles with diazoacetates catalyzed by a Cu(I) macrocyclic pyridine‐containing ligand (PcL) complex

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A highly reactive and selective catalytic system comprising Cu(I) and a macrocyclic pyridine‐containing ligand (Pc−L) for the synthesis of 2‐(penta‐2,4‐dien‐1‐ylidene) 3‐oxoindolines from 4 H ‐furo[3,2‐ b ]indoles and diazoalkane is reported herein. The reaction sequence involves the initial formation of a copper‐carbene by Cu(I)‐catalyzed decomposition of a diazoalkane followed by copper‐carbene to furoindole addition and successive furan ring‐opening affording the final products. The reaction proved to be quite general, tolerating EWG as well as EDG substituents on the indole scaffold as well as acceptor or donor/acceptor carbene precursors and products were obtained in good to excellent yields. The proposed methodology allows to overcome some selectivity issues encountered performing similar transformations in the presence of gold(I)‐carbenes. Interestingly, two of the 2‐alkenylidene‐3‐oxoindolines are characterized by a second‐order nonlinear optical response higher than that of Disperse Red One