Photochemical Approach to Fused Quinoxaline Derivatives From Allomaltol‐Containing Terarylenes With 2‐Aminooxazole Bridge Fragment via Trapping of Unstable Cyclopentene‐1,2‐Dione Intermediates

Abstract

The photochemical behavior of terarylenes bearing allomaltol and 2‐aminooxazole fragments has been investigated, providing the basis for an efficient strategy toward substituted cyclopenta[b]quinoxalines. Upon irradiation of starting compounds with 400 nm visible light, the allomaltol moiety undergoes selectively ESIPT‐induced contraction of the pyranone ring, affording highly reactive α‐hydroxycyclopentene‐1,2‐dione intermediates, as evidenced by 1 H NMR monitoring. Notably, the free amino group does not inhibit the photorearrangement, in contrast to related amino‐substituted terarylenes. In situ trapping with 1,2‐phenylenediamines affords cyclopenta[b]quinoxaline derivatives in yields of up to 87%, while phenylhydrazine gives separable E/Z hydrazones. The one‐pot protocol proceeds under mild, metal‐ and base‐free conditions.