Intramolecular Pd-catalyzed carbocyclization, Heck reactions, and aryl-radical cyclizations with planar chiral arene tricarbonyl chromium complexes

(o-butenqlhalobenzene) Cr(CO)(3) complexes were synthesized by diastereosel ectve allylmetal additions to o-halo benzaldehyde complexes. The addition o f allylZnBr proved particularly convenient and clean. The complexes undergo intramolecular Pd-catalyzed cyclizations (Heck reactions) without decomple xation and/or alkene isomerization. In complexes with a benzylic stereogeni c center, the diastereoselectivity of the alkene carbopalladation is govern ed by the planar chirality of the complex rather than by the benzylic stere ogenic center in the side chain. This reaction outcome can be rationalized by the geometry of the arene plane vs that of the Pd coordination plane in the transition step of the alkene carbopalladation step. An alternative cyc lization procedure involves the generation of a Cr(CO)(3)-coordinated arene radical from the bromo and iodo complexes. Intramolecular aryl-radical cyc lization affords indan complexes. The transition metal arene pi -bond remai ns intact during this process.