Optimization studies were performed on the model cross-coupling reaction of p-methoxyphenyl cyclopropanol 1a with electrophilic benzylidene malononitrile 2a under ultraviolet light (370 nm) irradiation (Table ; see also Table in the Supporting Information for additional data). The experiments were carried out in a 3D printed reactor designed by Noёl group and equipped with a Kessil lamp (43 W at 100% light intensity). Previously reported conditions (2 mol% TBADT, acetonitrile) were employed in the initial experiment (entry 1) which delivered ketone 3a in 84% yield after 3 h of irradiation. However, slightly improved 88-90% yields and shorter reaction time (1 h) were achieved at lower catalyst loading (1 mol%) when acetonitrile was replaced with dichloromethane (CH2Cl2) or acetonitrile/water mixture (entry 2 and 3). To confirm the photochemical nature of the process, a control experiment without light was carried out and no reaction occurred (entry 4). Moreover, the reaction was sensitive to the light intensity, as the conversion decreased when the lamp was used at lower power output (see Table in the Supporting Information). Surprisingly, 3a was obtained in 25% yield even in the absence of the photocatalyst (entry 5) indicating a plausible slower reaction via EDA complex of 1a and 2a (see discussion below). However, TBADT was crucial to accelerate the reaction and benzophenone (10 mol%) as an alternative photocatalyst afforded 3a in only 44% yield (entry 6). Table . Optimization of the reaction conditions. Entry Deviations Yield, % With the optimal reaction conditions established (CH2Cl2 as a solvent, 1 mol% TBADT), we explored the scope of different cyclopropanols in their photocatalytic cross-coupling reactions with benzylidene malononitrile 2a (Scheme 2, a). Cyclopropanols with electron-rich aromatic substituents afforded β-functionalized ketones in 56-87% yields (compounds 3aa-3ia). Among them, cyclopropanols 1b and 1c with MeO-substituents in meta-and ortho-positions gave the respective products 3ba and 3ca in lower 61% and 56% yields compared to para-methoxyphenyl cyclopropanol (3aa, 87% yield), which could be caused by steric factors or somewhat different electronic properties. For the reactions yielding m-OMesubstituted 3ba and 2-naphthyl derivative 3da, acetonitrile/water mixture was more beneficial reaction media compared to CH2Cl2, in which lower yields were obtained (e.g., 71% vs 59% for 3da). Notably, pyrrolyl and thiophenyl substituents tolerated the reaction conditions and the corresponding products 3ha and 3ia were obtained in 57% and 88% yields, respectively. The reaction with cyclopropanol 1j, bearing an electron-withdrawing p-trifluoromethyl group, afforded the product 3ja in a moderate 54% yield. However, less electron-deficient p-chlorophenyl cyclopropanol 1k was a successful substrate, which produced the corresponding adduct 3ka in excellent 92% yield. By contrast to aryl-substituted cyclopropanols 1a-k, alkyl and alkenyl cyclopropanols 1l-p and were less reactive and afforded the respective products 3la-3pa in low to moderate yields (42-61%) after significantly longer reaction time (20-48 h; Scheme 2, b). Thus, in the reactions of alkenyl cyclopropanols, 3na was produced from 1-cyclohexenyl cyclopropanol 1n in a low 41% yield. Styryl cyclopropanol 1o behaved similarly resulting in the formation of 3oa in 42% yield. N-Boc-protected cyclopropanol 1p was a competent substrate that produced 3pa in 40% yield, while its N-benzyl analogue 1r was incompatible and resulted in a complex mixture in which no respective cross-coupling product was detected. Additionally, we found that oxidants such as N-fluorobenzenesulfonimide (NFSI) or potassium persulfate as substoichiometric additives (0.2-0.5 equiv.) can improve yields, accelerate, or even trigger the reaction of otherwise unreactive cyclopropanols. For instance, compound 3la was obtained in 63% yield after 3 h with NFSI additive (0.5 equiv.) while the standard conditions delivered only 53% yield after 20 h. Similarly, n-amylcyclopropanol 1q was converted into the corresponding ketone product 3qa. Besides highly electrophilic alkene 2a, 2-phenylethyl cyclopropanol 1l was also able to react with dimethyl fumarate 2f and diethyl benzylidenemalonate 2k, affording the respective products 3lf and 3lk in 58% and 40% yields, while only traces of the products were formed without NFSI additive.