Past exam of the chemistry course of the year 4 of the natural sciences course of the University of Cambridge / 2022 / Paper 1 / 9 / b / ii / Solution

The analogous N-oxide rearrangement uses the carbon next to nitrogen that most readily supports addition and rearomatization. In isoquinoline this is C1. Thus replace the quinolin-2-yl group of D by isoquinolin-1-yl:The ynone-to-chromone atom mapping is unchanged. The change is attachment at isoquinoline C1, rather than copying quinoline numbering and assigning an isoquinolin-2-yl carbon substituent at the nitrogen position.