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Ruthenium(0) Catalyzed Endiyne−α-Ketol [4 + 2] Cycloaddition: Convergent Assembly of Type II Polyketide Substructures via C–C Bond Forming Transfer Hydrogenation

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journal contribution
posted on 13.05.2015, 00:00 by Aakarsh Saxena, Felix Perez, Michael J. Krische
Upon exposure of 3,4-benzannulated 1,5-diynes (benzo-endiynes) to α-ketols (α-hydroxyketones) in the presence of Ru(0) catalysts derived from Ru3(CO)12 and RuPhos or CyJohnPhos, successive redox-triggered C–C coupling occurs to generate products of [4 + 2] cycloaddition. The proposed catalytic mechanism involves consecutive alkyne-carbonyl oxidative couplings to form transient oxaruthanacycles that suffer α-ketol mediated transfer hydrogenolysis. This process provides a new, convergent means of assembling Type II polyketide substructures.