A Stereoselective, Base-free, Palladium-Catalyzed Heck Coupling Between 3-halo-1,4-Naphthoquinones and Vinyl-1H-1,2,3-Triazoles

A stereoselective, base-free Heck coupling between 1,4-naphthoquinone and 1H-1,2,3-triazole derivatives was reported for the first time. This study shows that depending on the 1,4-naphthoquinone, the use of an additional base is unnecessary to produce the naphthoquinone-triazole conjugates. This is also the first example of a Heck coupling of these two cores without using a base as an additive. In this work, sixteen new naphthoquinone-triazole hybrids were stereoselectively synthetized in good to excellent yields. The reaction mechanism was discussed based on DFT CAM-B3LYP calculations. The first step is the coordination of the arene to the palladium catalyst to form a palladacycle intermediate. After reorganization in this intermediate, the double bond in the arene is restored to proceed with the coupling step and formation of the C-C bond in the rate determining step. The Kozuchi-Shaik span model was employed to rationalize substituent effects.

Automated summary

A stereoselective and base-free Heck coupling between 1,4-naphthoquinone and 1H-1,2,3-triazole derivatives was reported for the first time. This study demonstrates that the use of an additional base is unnecessary for the synthesis of naphthoquinone-triazole conjugates. The reaction mechanism and substituent effects were also discussed in this work.