Metal-Mediated Routes to Biaryls

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DESCRIPTION (provided by applicant): Biaryls represent a major area of natural and unnatural products chemistry. Given the widespread occurrence of physiologically active compounds in Nature that contain a biaryl axis, many of which due to hindered rotation possess an element of axial chirality, methodology is needed to respond to these special synthetic challenges. Representative targets which highlight existing limitations yet which provide opportunities for significant advances in this area include the clinically essential antibiotic vancomycin, and the potent anti-AIDS biaryls, the michellamines. Using a judiciously placed internal phosphine ligand in an aryl halide coupling partner, the directionality associated with our key Suzuki-biaryl coupling-based approach to the vancomycin biaryl and the subunits of the michellamines will be controlled. Alternatively, a conceptually new entry to stereocontrolled biaryls, as applied to vancomycin, will be pursued using a Bergman cyclization of a substituted nonracemic endiyne. The chemistry of biaryl constructions, which is usually effected in solution using Pd(0) catalysis, is to be pursued via an alternative metal system: nickel. Proposed herein are new methods for heterogeneous catalysis based on Ni/C, to be examined under microwave conditions, and the next generation species nickel-on-graphite ("Ni/Cg"), which appears to offer a different reactivity profile. Finally, a new series of nonracemic ligands based on the binaphthyl core, in particular of NOBIN, will be constructed. The approach presented will provide entry to unprecedented substitution patterns on this ligand system, as well as opportunities for their mounting on a solid support for use, and re-use, under heterogeneous conditions. A particular, albeit representative, application of a novel substituted cyclo-NOBIN will be studied for selected asymmetric aldol reactions.