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

[GRAPHICS] A highly efficient and stereoselective protocol for the syntheses of symmet rical and unsymmetrical carotenoids involving Zr-catalyzed carboalumination of conjugated oligoenynes and Pd- and Zn-catalyzed alkenyl-alkenyl couplin g has been developed and applied to the syntheses of beta- and gamma -carot ene and vitamin A. gamma -Carotene of greater than or equal to 99% isomeric purity was prepared in three linear steps (five steps overall) from beta - ionone, enyne 8, (E)-ICH=CHBr, and (E)-Me3SiC=CCH=CHBr in 32% overall yield .