Scheme 2. Scope of the photocatalytic crossed [2 + 2] cycloaddition. Reactions were performed on 0.20 mmol scale. Yields refer to isolated material after flash column chromatography. S = substituent position. a Yield estimated from the 1H NMR spectrum of the reaction mixture relative to 1,3,5-trimethoxybenzene as internal standard. b Isolated together with unreacted diene 1l. c 66 h reaction time. Displacement ellipsoids are drawn at 50% probability level.
