The synthesis of 1,1-disubstituted and tri-substituted vinylboronate esters with control of the alkene stereochemistry remains a challenge in organic synthesis. Typical methods require harsh reaction conditions or have limited substrate scope due to issues of stereoselectivity. In this paper we report facile formation of these valuable synthetic intermediates in a two-step, one flask procedure from ketones. The copper-catalyzed diboration of ketones followed by acid-catalyzed elimination leads to the formation of 1,1-disubstituted and tri-substituted vinyl boronate esters with moderate to good yields and high selectivity. Copper-catalyzed diboration of ketones is mediated by 3 mol % copper catalyst [(ICy)CuCl] (ICy = dicyclohexylimidazolyl), 5 mol% base (NaOt-Bu), and bis(pinacolato)diboron. Addition of tosic acid to the crude diboration product provides vinyl boronate esters. Formation of vinyl boronate esters though this method provide moderate to good yield (41% to 79%) and high selectivity over two steps. The solvent used in the elimination step was found to have a substantial effect on the yield and selectivity of alkene formation. The results suggested that toluene provided lower selectivity than dichloromethane in the elimination step, but were much more consistent in product formation. Progress on the Suzuki-Miyaura coupling of these vinyl boronate esters and identification of the major olefin isomers with be discussed.

Diboration/elimination of ketones: Facile synthesis of 1,1- and tri-substituted vinyl boronate

246th National Meeting (2013)

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