Irradiation of 2‐(ω‐alkenoyl)‐1,2‐dihydroisoquinoline‐1‐carbonitriles (Reissert compounds) with blue light‐emitting diodes ( λ = 455 nm) in the presence of an iridium‐based photocatalyst efficiently afforded cyclobutane‐fused benzo b quinolizinone derivatives in high yields and with moderate to high stereoselectivity. A catalyst loading as low as 0.5 mol% was sufficient to drive the reaction to completion within 1 h in many cases. Mechanistic studies suggest that the transformation proceeds via a stepwise 2 + 2 cycloaddition pathway involving a triplet biradical intermediate.
Arai et al. (Sun,) studied this question.