Next, we explored the scope of the photochemical ring contraction from 1a to dihydro-4H-cyclobuta [c]isochromenes, to elucidate the influence exerted by substituents in other 1H-2-benzo [c]oxocin analogues (Figure ). To our delight, all 1H-2benzo [c]oxocins with aromatic groups at the enol ether R1position converted to dihydro-4Hcyclobuta [c]isochromenes with great efficiency using visible light (Figure ; Figure ). While modification of 1a to interrogate the effect of various substituents and positions demonstrate no noticeable influence on the reactivity, 8-membered rings with aliphatic substituents at the enol ether R1-position (Figure 2B, 13b-19b; Figure 2D, 22b-23b) experience low isomerization efficiency when using white light. For these compounds, it was necessary to change the light source to UV light (365 nm) in order to achieve full conversion (Figure ; Figure ).