| A palladium(0) catalyst has been employed in heteroannulation and ternary coupling reactions that form important functionalities, as well as in migration chemistry which has never before been observed.; Firstly, a palladium(0) catalyst was employed to affect the heteroannulation of o-amino- and o-hydroxyaryl iodides onto cyclic and bicyclic alkenes, which prevent β-hydride elimination in the key organopalladium intermediate. The heteroannulation of o-aminoaryl iodides onto alkenes employed different conditions than the heteroannulation of o-hydroxyaryl iodides. The reaction appears to involve: (1) oxidative addition of the carbon-iodide bond of the aryl iodide to the palladium catalyst, (2) arylpalladation of the olefin carbon-carbon double bond, (3) possible coordination of the internal nucleophile to the palladium, (4) formation of a six-membered palladacycle by loss of hydrogen iodide, and (5) reductive elimination of the organopalladium intermediate to regenerate Pd(0) and the heteroannulation product.; Secondly, the construction of tetrasubstituted alkenes by a palladium(0)-catalyzed procedure involved the ternary coupling of aryl iodides, alkynes, and organometallics. These reagents presumably form the alkene by: (1) oxidative addition of the aryl iodide to the palladium(0), (2) carbopalladation of the alkyne, (3) transmetallation between palladium and the organometallic (e.g. a boron, tin, or silicon organometallic), and (4) reductive elimination of the tetrasubstituted alkene with simultaneous regeneration of the Pd(0) catalyst.; Thirdly, the Larock group has produced standard palladium migration conditions, which were employed in an investigation of this new chemistry. Although these conditions were optimized by varying the base, ligand, and solvent, these standard conditions proved satisfactory for palladium migration to occur. Various examples of this reaction are presented where the palladium has presumably migrated from an aryl group to an acyl group. |
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