In this project funded by the Chemical Synthesis Program of the Chemistry Division, Professor Amir H. Hoveyda of the Department of Chemistry at Boston College will develop catalytic methods for selective synthesis of boron-containing organic molecules as well as protocols that utilize such entities in bond-forming processes. Specifically, catalytic methods for site-, diastereo- and enantioselective hydroborations of trisubstituted olefins, of internal alkynes as well as the resulting trisubstituted vinylboronates, will be developed. Enantioselective reactions will be promoted by chiral N-heterocyclic carbene-copper (NHC-Cu) complexes. NHC-Cu catalysts will also be utilized in hydroborations of internal alkynes with emphasis on accessing the more sterically hindered vinylboronates, which cannot be synthesized by other catalytic or uncatalyzed reactions. Additionally, reactions involve addition of Cu-B across alkynes, the resulting B-substituted vinylcoppers will be utilized in tandem enantioselective C-C bond forming processes through allylic substitution or conjugate addition reactions (vs Cu-C protonation to afford hydroboration product). These new Cu-catalyzed processes will allow access to a wide range of enantiomerically enriched carbo- and heterocyclic structures that bear a tertiary alcohol stereogenic center and a trisubstituted vinylboronate. Finally, catalytic inter- and intramolecular Cu-catalyzed ketone vinyl additions will be developed wherein vinylboronates, accessed in situ by Cu-catalyzed hydroborations mentioned above, serve as the source of the vinylcopper. Readily accessible and air stable vinylboronates will be utilized, instead of other less functional group tolerant vinylmetals, in new ways for preparation of a wide range of acyclic and cyclic tertiary allylic alcohols with high enantioselectivity.
Development of new methods that allow access to important molecules that are otherwise difficult to prepare is a central objective of research in modern chemistry and is therefore of substantial value; such developments require fundamental advances in chemistry and thus positively impact future efforts in other areas of catalyst design. Of particular importance are transformations that proceed with high site- and chemoselectivity and are initiated by a readily accessible catalyst that delivers products predominantly consisting of a single diastereo- and/or enantiomer. Within this context, the introduction of general protocols for catalytic and selective synthesis of B-containing organic molecules, such as hydroborations of alkenes or alkynes, stands as a compelling goal in chemical synthesis; the resulting C-B bonds may be converted to C-O, C-N or C-C bonds with retention of sterechemistry, adding further value to such processes. The proposed activities will serve to train numerous young scholars, including those from historically underrepresented in physical sciences, at a wide range of development stages. High school, undergraduate, graduate and postdoctoral fellows, actively involved with the experimental as well as intellectual aspects of our investigations, will gain the skills necessary to become future leaders in industry as well as the academic sector.