An approach to access 1-substituted isoquinolones has been developed through the addition–cyclization of imines with Grignard reagents in the presence of 2,2′-dipyridyl. A number of substituted aromatic magnesium reagents were amenable to this process, and the desired products were obtained with excellent yields and outstanding diastereoselectivities (dr > 99:1). The utility of this convenient approach