Ruthenium(0)‐Catalyzed [4+2] Cycloaddition of Acetylenic Aldehydes with α‐Ketols: Convergent Construction of Angucycline Ring Systems

Ruthenium(0) complexes modified by CyJohnPhos or RuPhos catalyze the successive C−C coupling of acetylenic aldehydes with α-ketols to form [4+2] cycloadducts as single diastereomers. This method enables convergent construction of type II polyketide ring systems of the angucycline class.