The first investigated reaction was the energy transfer-catalyzed [2+2] cycloaddition depicted in Table that was first published in a racemic fashion in 2020 by the group of Yoon. In the achiral version, a ruthenium catalyst can only effectively excite the imidazole substrate 13 in the presence of the acid p-TsOH (20 mol%), as the acid co-catalyst facilitates the triplet energy transfer of the photocatalyst (Table , entries 1-4). A year later, the group published a chiral version of this reaction utilizing 1 mol% of [Ir(Fppy)2(dtbbpy)]PF6 as photocatalyst with 20 mol% chiral BINOL-derived phosphoric acids CPA-1 and CPA-2 (entries 5-7). At room temperature, their initial conditions utilizing CPA-1 resulted in 72% yield with 37% enantiomeric excess (ee) and a diastereoselective ratio (d.r.) of 1:2 favoring the trans-trans 14 over the trans-cis product 14 (entry 5). Interestingly, when switching to the more acidic N-triflyl phosphoramide derivative of the chiral acid (CPA-2), they observed that no photocatalyst is needed at all and they can achieve similar yields via direct excitation with 20 mol% acid in high ee (97%) and high, but reversed, d.r. (6:1 for the trans-cis product) when the temperature is lowered to -78 °C (entry 8). Utilizing solely 5 mol% of PCI with the same solvent system as reported by the Yoon group, an ee of 35% was achieved at room temperature (entry 9) with a yield of 70% while slightly favoring the transtrans product 14 with a d.r. of 1:1.3 (trans-cis:trans-trans). This result is comparable to the results achieved by the Yoon group at room temperature using their dual catalytic system (see above Table , entry 5). PC II achieves similar yields (72%), albeit with a slightly lower enantioselectivity of 27% ee at room temperature but with better diastereoselectivity of 1:1.6 favoring the trans-trans product of 14 (entry 11). As higher enantiomeric values and better d.r.'s were observed by the Yoon group when lowering the reaction temperature to -78 °C, we investigated the effects of low temperature for our catalysts as well (entries 10 and 12). We were delighted to find that upon lowering the temperature to -78 °C, both photocatalysts gave improved enantioselectivities, with PCII producing 65% ee with a simultaneously improved yield of 80% (entry 12). As observed in the original publication by the Yoon group, the diastereoselectivity also improved, now favoring the trans-cis product of 14 with a moderate d.r. of 3.8:1.