We hypothesized the formation of 2a in only low yield was due to limited oxygen solubility, because the reaction under N 2 protection led to a purple coloration in the post-reactor reaction mixture (see SI), an observation consistent with the formation of DCAS •-. When the purple post-reactor reaction mixture was collected and exposed to air, immediate discoloration back to yellow was observed. We note that the related parent structure DCA •-is well-known to be purple in color. Since the solubility of O 2 in an O 2 -saturated solution of MeCN is 8.1 mM and considering the requirement of 2 equiv. O 2 , 80,81 mass transfer limits full conversion of a reaction mixture of 12.0 mM amine. Studies using a gas-liquid flow photoreactor. In lieu of the abovementioned observations, we opted for a photoreactor designed for biphasic gas-liquid reactions. A commercial microfluidic continuous flow photoreactor (Corning Lab Photoreactor © ) designed for excellent mixing achieves turbulent slug flow and allows safe operation up to 60 o C and 8 bar backpressures to access homogeneous conditions with higher dissolved O 2 . The hazard of the flammable reaction mixture is safely contained by the thermal isolation of the flow path and the small volume of reaction mixture (2.7 mL) at any given time. A summary of reaction condition optimization is shown in Table (see SI for full optimization). Under conditions mirroring entry 5 from the previous reactor, 2a was afforded in 22% yield (entry 1), as expected since the decrease in yield is consistent with (proportional to) the decreased residence time. However, the yield almost doubled when 395 nm LEDs were used (entry 2), which accorded with the higher intensity of the UV-vis band of DCAS at ca. 395 nm compared to the 420 nm band (vide supra). At 24 mM 1a and double the residence time, the yield increased to 44% (entry 7). At 48 mM of 1a the yield decreased to 24% (entry 8), presumably due to the reaction solution reaching saturation which competed with O 2 solubility. At T = 60 o C and 24 mM 1a, the yield of 2a marginally improved to 46% (entry 9). The inherent back pressure on the flow by the microfluidic module was sufficient to ensure precise, reproducible, low flow rates (down to 0.1 mL/min) up to 60 o C. To our delight, tropine 1b afforded 2b in 60% under reaction conditions at T = 40 o C and R T = 27 min (entry 10) despite its free 2 o alcohol typically prone to oxidation under similar oxidative conditions. Decreasing catalyst loading decreased the yield (entries 11 and 12). Similarly to the case of substrate 1a, a marginal increase of yield to 61% occurred at 60 o C (entry 13). At this stage, we explored the effect of a back pressure (8 bar) to evaluate higher O 2 solubility (entries 14-16). While doubling concentration to 48 mM or using a residence time as short as R T = 6.8 min negatively impacted the yield of 2b (entries 14-15), we found that yield was preserved at a residence time of R T = 13.5 min (entry 16). This doubled productivity of 2b to 0.65 g /day. Next, we tested the scope of the reaction (Table ). Since isolations of polar formamides were oftentimes challenging and involved a weak chromophore, the following discussion deems 1 H NMR yields more representative of reaction efficiency. Compounds 2c (59%) and 2d (67%) were obtained from natural products Tropane and (free alcohol-bearing) Atropine. Even Scopolamine, which has a free alcohol, ester, and an epoxide, afforded 2e in 62% yield with no nor-scopolamine detected, albeit requiring 2 passes through the reactor (total R T = 27 min). This contrasts with Santamaria and co-workers' conditions using DCA and without LiClO 4 , which afforded a 1:1 mixture of 2e : norscopolamine. Compared to 2b, the yield of 2f was lower (34%) presumably due to the presence of the Si protecting group (DPMS) known to stabilize radicals and quench excited photosensitizers via different pathways. Benzoyl-containing compound 2g was afforded in good yield 73%. Electron poor (CF 3 ) and electron rich (-OMe) substituents on the benzoyl group were tolerated equally, affording 2h (56%) and 2i (58%) respectively. We note both 2g and 2i are natural products; novel tropanoid compound 2g was recently isolated from Pellacalyx saccardianus and this synthetic method corroborated the proposed structure. Compound 2g (Confoline) was isolated from Convolvulus subhirsutus and our method accessed it from Convolvamine in a single step. (in the literature, semi-synthesis of 2i was achieved by formylation of demethylated Convolvamine). Compounds 2j to 2o were obtained from piperazines as common API fragments (such as those present in Sildenafil and Danofloxaxin). Despite having 3 possible sites for functionalization (one exocyclic N-CH 3 and two endocyclic N-CH 2 -R sites), selective N-CH 3 oxidation afforded N-formyl compounds in respectable yields. We were surprised by the tolerance of halogen-bearing substrates, affording 2l (55%), 2m (21%), and 2n (30%) (as well as 2h) under the reaction conditions. Formation of DCA •-is well-known via the reductive quenching of 1 DCA* by trialkylamines together with our aforementioned detection of the characteristic purple coloration of DCA •-under the reaction conditions. Photoexcited radical anions are known to facilitate reductive cleavages of aryl halides and other strong bonds, while C-F bonds and N-Ts groups are prone to cleavage under reductive photocatalysis or by photoexcited super electron donors. Simple piperidine 2p (39%) was also tolerated. Our success with 2b, 2d, 2e, and 2p whose substrates bear free alcohol groups encouraged us to explore more complex molecules. Gratifyingly, conditions were successfully applied to macrolide antibiotics with dense functionalities (free alcohols, oxime ether, ketone). Erythromycin, clarithromycin and roxithromycin afforded 2r, 2s, and 2t in 61%, 44%, and 24% yields, respectively. However, compounds bearing benzylic amines, benzylic -hydroxy amines (separated by conformationally free rotating -bond), free carboxylic acids, and olefins such as 1u, 1v and 1w were unsuccessful. Benzaldehyde formation (C-N cleavage, possibly via endocyclic iminium ion formation and hydrolysis) and complex reaction mixtures were observed for these substrates.