Fig. 1. Reaction scope^a,b – ^aIsolated yields of experiments on 0.2–0.5 mmol scale, unless otherwise noted. ^bReactions afforded 13 as a single diastereomer, unless otherwise noted. ^cn-BuOH was used in place of MeCN. ^dYield of a gram-scale reaction. ^eThe C₂ epimer was isolated in 26% yield and >20 : 1 d.r. when n-BuOH was used as the solvent. ^fYield was determined by ¹H NMR using N-benzylbenzamide as an internal standard. ^gSubstrate 12h required 24 h in the photoreactor to achieve a 27% conversion to the corresponding [2 + 2] photoadduct (see the ESI for details†).