Visible-light induced copper(i)-catalysed denitrogenative oxidative coupling of hydrazinylpyridines with terminal alkynes

Abstract

Visible light mediated copper catalysed denitrogenative oxidative coupling of 2-hydrazinopyridines with terminal alkynes to form 2-(alkyl/arylethynyl) pyridines in the presence of O₂ at room temperature is reported with 42 examples. This is the first report on visible light stimulated N₂ elimination by an in situ generated copper(II) superoxo/peroxo complex. N₂ and water are the only by-products. The green chemistry metrics evaluation signifies that the current method is ecofriendly and economically feasible. This method allows the green synthesis of mGluR5 receptor antagonists, 2-methyl-6-(phenylethynyl)pyridine (MPEP) and 2-((3-methoxyphenyl)ethynyl)-6-methylpyridine (M-MPEP).