Enantioselective synthesis of polycyclic carbocycles via an alkynylation-allylation-cyclization strategy.

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A new general three-stage strategy to access polycyclic ring systems bearing all-carbon quaternary centers with high enantioselectivity is reported. The required starting materials were readily accessed in racemic form through the α-alkynylation of ketoesters with EBX (EthynylBenziodoXolone) hypervalent iodine reagents. A Pd-catalyzed asymmetric decarboxylation allylation was then achieved in high yields and enantioselectivities with Trost's biphosphine ligands. Finally, transition-metal catalyzed cyclization of the obtained chiral enynes gave access to fused and spiro polycyclic ring systems constituting the core of many bioactive natural products.