An unusual rearrangement involving 5-bromo-1-phenylpyridone during its methyl cross coupling with turbo-Grignard reagent, leading to a 5-bromopyridone-fused seven-membered carbocyclic ring

The structure of a cyclohepta[ c ]pyridin-1-one, a product of an unusual transformation, isolated during a turbo-Grignard reagentpromoted methyl cross coupling to 5-bromo-1-phenyl-2-pyridone, was determined by 1 H and 13 C NMR, COSY and high-resolution MS, as well as computer modeling. Its formation suggests a remarkable nucleophilic attack at the α-position to the pyridone carbonyl group. A rational pathway is presented.