Total synthesis of (+)-gregatin B and E.

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 of γ-propynyl-1,3-diketones with palladium(II)-bisoxazoline catalyst.

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.