Development and Applications of Asymmetric Hydrovinylation of Alkenes

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DESCRIPTION (provided by applicant): By every measure the demand for enantiomerically pure intermediates for the synthesis of chiral pharmaceutical products keeps mounting. Discovery of new asymmetric reactions, especially those which would yield practical levels of asymmetric induction and high turnover frequencies (i.e., substrate/catalyst/unit time), will have significant impact on medicinal as well as process chemistry. Through an approach that relies primarily on mechanistic insights and systematic examination of ligand effects, we have discovered a number of protocols for the enantioselective heterodimerization reactions of ethylene with vinylarenes, 1,3-dienes and strained olefins. We have also uncovered reactions for the asymmetric generation of all-carbon quaternary centers, which are otherwise difficult to install. Mild reaction conditions, tolerance to various functional groups, isolated yields >95%, substrate/catalyst ratios of 100-1000 and enantioselectivities of 90-99% ee for various reaction imply that hydrovinylation could be developed into a practical process for the synthesis of molecules with a chiral 3-(alkyl or aryl)-1-butene motif. Many biologically important molecules can be easily accessed from these intermediates. Examples illustrated include powerful anti-inflammatory, antitumor and antituberculosis agents. In some cases these are the first enantioselective syntheses, while in others, where analog synthesis could benefit clinical studies, the relative merits of this approach vis-a-vis known methods are pointed out. Broadly, the goals of this project are two fold: (a) Improvements in the selectivity and scope of hydrovinylation. Following our preliminary results, we want to explore and expand the scope, and applications of the hydrovinylation of vinyl arenes, 1,3-dienes and strained olefins, including those give chiral all-carbon quaternary centers. This would involve the discovery of new protocols, and of new chiral ligands for this exacting reaction, (b) Application of asymmetric hydrovinylation in total synthesis of natural products. A general solution to the classical problem of installation of exocyclic chiral centers will be illustrated with synthesis of (-)-laurenditerpenol, steroid C/D ring analogs, helioporins and pseudopterosins and serotonin antagonist LY426965. Stereoselective syntheses of these compounds are especially important because of their varied biological activities (including cytotoxic, anti-inflammatory and antimycobacterial properties), dependence of such activities on the configuration of each of the chiral centers, and paucity of methods for absolute stereochemical control in C-C bond formations. Hydrovinylation offers outstanding opportunities in this regard. Applications aside, we hope that the study of the reaction would reveal new control elements useful for the development of new, broadly applicable, tools for catalytic asymmetric synthesis.