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

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 4H-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.