Rhodium-Catalyzed Synthesis of 3-Aryl and 3-Alkenyl Phthalides

Significance

Based on the phthalide synthesis by Dong and co-workers via enantioselective aldehyde C-H functionalization (J. Am. Chem. Soc. 2009, 131, 15608), the present work deals with the rhodium-catalyzed addition of arylboronic ­acids to phthalaldehyde to afford 3-aryl- and 3-alkenylphthalides in moderate to good yields. The ­optimal reaction conditions require the use [{Rh(cod)Cl}₂] as a catalyst in association with dppb as a ligand and K₂CO₃ as a base in 1,2-dichloroethane. These conditions promote reactions with a range of substituted arylboronic acids. Boronic acids bearing electron-donating groups generally afford the corresponding phthalides in higher yields than those with electron-withdrawing groups. Several plausible mechanisms are proposed without evidence.