Light-Mediated Synthesis of 2-(4-Methoxyphenyl)-1-pyrroline via Intramolecular Reductive Cyclization of a Triplet Alkylnitrene.

Irradiation of -methoxyazidobutyrophenone () in methanol yielded 2-(4-methoxyphenyl)-1-pyrroline () and several other photoproducts. However, in the presence of tris(trimethylsilyl)silane (TTMSS), is formed selectively. Transient absorption and ESR spectroscopy verify that the irradiation of forms triplet alkylnitrene through intramolecular energy transfer from the triplet ketone (T). DFT calculations indicate that abstracts H atoms from TTMSS but not methanol, which explains the selectivity. Thus, triplet alkylnitrenes can undergo selective reductive cyclization via H atom abstraction from TTMSS.