One-shot photochemical synthesis of 5-(thiophen-S-yl)pyrano2,3-cchromen-2(3H)-ones from 3-propynyloxy-chromenones: a case of an intramolecular Paterno-Buchi reaction

摘要

5-(Thiophen-3-yl)pyrano2,3-cIchromen-2(3H)-ones (2), angular tricyclic compounds, were synthesized in significantly high yields through the photoinduced intramolecular coupling of the acetyle-nic group with the carbonyl centre in 3-(prop-2-ynyloxy)-2-(thio-phen-3-yl)-4H-chromen-4-ones (1). This photoreaction is a case of an intramolecular Paterno-Buchi reaction and is unprecedented in 3-propynyloxy-chromenones. The structure of 2 has been determined by spectroscopic (FTIR, NMR and mass) and single crystal X-ray crystallographic studies.