Visible-Light-Promoted Photoaddition of <i>N</i>‑Nitrosopiperidines to Alkynes: Continuous Flow Chemistry Approach to Tetrahydroimidazo[1,2‑<i>a</i>]pyridine 1‑Oxides

The photoaddition of <i>N</i>-nitrosopiperidines to terminal alkynes was effected under visible-light irradiation, in which a novel synthetic access to tetrahydroimidazo­[1,2-<i>a</i>]­pyridine 1-oxides was achieved via the dehydrogenative cycloisomerization of β-nitroso enamine intermediates. The decomposition pathways of <i>N</i>-nitrosamines, alkynes, and β-nitroso enamine intermediates were better handled in a continuous flow setting through the diffusion control of chemical species that negatively affected the formation of tetrahydroimidazo­[1,2-<i>a</i>]­pyridine 1-oxides under batch reaction conditions.