Cu-Catalyzed Conjugate Addition of Grignard Reagents to Thiochromones: An Enantioselective Pathway for Accessing 2-Alkylthiochromanones

The enantioselective incorporation of alkyl groups in thiochromones was realized for the first time by a Cu/(R,S)-PPF-P t Bu2-catalyzed conjugate addition of Grignard reagents to thiochromones. With this method, a series of 2-methylthiochromanones were obtained in good yields (up to 96% yield) with moderate-to-good ee values (up to 87% ee). The established method expedites the synthesis of a large library of chiral thiochromanones for further synthetic applications and biological studies.