We optimized the reaction conditions aiming to maximize the yield of 2a, with this cis-product offering greater potential for downstream diversification. Initially various bases were investigated at 110 °C. Acetate salts biased the reactivity towards the preferential formation of 2a, albeit in modest yields. A breakthrough in selectivity was achieved on significantly lowering the temperature. Chen had previously reported monoarylation of cyclopentanes at ambient temperature using chlorinated solvents. Reacting 1 with K2CO3 in CH2Cl2 gave <5% yield (entry 2) whereas Ag2CO3 gave 2a exclusively in an encouraging 33% yield over 72 h (entry 3). A range of solvents were screened, including substituted aromatics, alcohols and polar aprotic solvents. Halogenated aliphatic and aromatic solvents afforded the highest yields of 2a (entries 3-7), and α,α,α-trifluorotoluene gave 40% of the mono-cis arylation exclusively (entry 7). Increasing the temperature in increments of 10 °C led to a peak of 48% yield at 45 °C (entry 8). Above this temperature the overall conversion could not be enhanced. Instead, formation of mono-trans 3a and diarylation to cis-trans 4a was encouraged at the expense of 2a. Having identified the reaction temperature as a crucial factor, we next examined the effect of additives to increase reactivity, aiming to reduce the reaction time (Table ). 27 a Reactions on 0.2 mmol scale. b Calculated by 1 H NMR spectroscopy using 1,3,5-trimethoxybenzene as internal standard. a Reactions on 0.2 mmol scale. b Calculated by 1 H NMR spectroscopy using 1,3,5-trimethoxybenzene as internal standard. Isolated yield in parentheses. c 2.0 equiv ArI, 1.25 equiv Ag2CO3, PhCF3 (0.3 M).