Access to pyrido-pyrimidinone and imidazopyridine <i>via</i> Fe(<scp>iii</scp>)-mediated denitrogenative annulation of tetrazolopyridine with β-keto ester

An iron(III)-mediated denitrogenative annulation of tetrazolopyridine with β-keto esters was developed to produce two classes of nitrogen-containing heterocycles; pyrido-pyrimidinone and imidazopyridine, and the selectivity of product formation was controlled by alkali metal halide salts present in the reaction medium. Mechanistic studies suggested that these reactions likely proceed <i>via</i> a radical mechanism. This single-step reaction yielded a diverse range of these N-heterocycles linked to different natural product scaffolds. A gram-scale synthesis was carried out to confirm the scalability of this method.