A novel, selective, and efficient route to carotenoids and related natural products via Zr-catalyzed carboalumination and Pd- and Zn-catalyzed cross coupling

structure: see text]. A highly efficient and stereoselective protocol for the syntheses of symmetrical and unsymmetrical carotenoids involving Zr-catalyzed carboalumination of conjugated oligoenynes and Pd- and Zn-catalyzed alkenyl-alkenyl coupling has been developed and applied to the syntheses of beta- and gamma-carotene and vitamin A. gamma-Carotene of > or =99% isomeric purity was prepared in three linear steps (five steps overall) from beta-ionone, enyne 8, (E)-ICH=CHBr, and (E)-Me3SiC triple bond CCH=CHBr in 32% overall yield.