An inhibitor (tert-butyl catechol)free liquid diene was mixed with 1,1-dinaphthylmethanone (photosensitizer used in the range of 0.1 -0.5 mol%). Two different volumes of reaction solutions were used in this study: 5 mL in all the experiments with neat dienes (>90 wt%); and 20 mL for reactions of diluted dienes (<60 wt%). A solution of diene and photosensitizer was then degassed by using freeze-pumpthaw cycles (3×) and left in an argon atmosphere. By using a syringe, the homogenous solution was then transferred to the coiled tube reactor (Teflon tube O.D. × I.D.: 3.18mm × 2.1mm, loop size ~20 mL, Fig. , ESI) 10 sealed with septa. The reactor had been previously purged with argon gas for 3 min. The coiled tube reactor was then connected to the chiller at a constant temperature (7 °C) to maintain the reaction at a low temperature to avoid the build-up of pressure or loss of starting material. Either an RPR-100 or -200 Rayonet Photochemical Chamber reactor were used for the photoreaction. The photochemical reaction was initiated under irradiation at 365 nm (Xenon lamp, 16 × 24 WUV lamp purchased from Southern New England Ultraviolet Company) and run for 24 h (if not mentioned otherwise). The light intensity in the reactor was approximately 8 mW/cm 2 (if not mentioned otherwise) as measured by a portable radiometer (spectral radiometer RM12 purchased from Opsytec). After the reaction time, the solution was passed through a silica gel column using pentane as the eluent.