Pd–NHC Catalyzed Biaryl Coupling by Direct C–H Activation—A Novel Strategy for the Synthesis of Dibenzocyclooctane Lignans

Abstract

Cross-coupling reactions, such as Buchwald-Hartwig arylamination and direct intramolecular biaryl coupling by C–H activation, were carried out using various Palladium-N-heterocyclic carbenes (Pd–NHC) as catalysts. The yields were good to excellent. The latter strategy was adopted to transform two dibenzylbutane lignans, isolated from the leaves of Ocotea macrophylla (Lauraceae), into the corresponding dibenzocyclooctane lignans in good overall yields.

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Keywords:

• Cross-coupling reactions
• dibenzylbutane
• dibenzocyclooctane
• lignans
• N-heterocyclic carbenes (NHC)

ACKNOWLEDGMENTS

The authors thank Umicore AG & Co. KG. for the donation of catalysts 1–3 and the Institut für Chemie, Universität Potsdam for analytical support. E. D. Coy acknowledges the DAAD (Deutscher Akademischer Austausch Dienst) for a scholarship at the Universität Potsdam.

Notes

^a Carried out to room temperature.

^b Carried out at 50 °C.

^c Carried out at 80 °C.

^d Yield of isolated product under anaerobic conditions (yield of isolated product under aerobic conditions).

^e Reported yield under anaerobic conditions according to Ref.^{[ 1 ]}

^a Yield of isolated product.

^b Reported yields according to Ref.^[7]