The first total synthesis of (+)-gregatin E and a new total synthesis of (+)-gregatin B are described. Key features of our synthetic approach involve a palladium-catalyzed cyclization-methoxycarbonylation of optically active propargylic acetate and a Suzuki-Miyaura coupling or CuTC-mediated coupling reaction. The absolute configuration of (+)-gregatin E (5R,5'S) is proposed.
Cyclization-carbonylation-cyclization coupling reaction (CCC-coupling reaction) of γ-propynyl-1,3-diketones catalyzed by (box)Pd(II) complexes afforded symmetrical ketones bearing two oxabicyclic groups in moderate to excellent yields.
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