Green-Light Photocatalysis: Borylated Benzo[c][1,2,5]thiadiazole (BTZ) Enables Phosphorylation of Quinoline Derivatives

A library of 10 novel organophotocatalysts (ORG-PRCs) has been prepared by the one-pot, two-step ortho-borylation of 4,7-diarylbenzo[c][1,2,5]thiadiazoles (BTZs). The borylation reaction was accompanied by a substantial bathochromic shift in both the absorption and emission spectra (up to 142 nm), allowing these photocatalysts to operate using low-energy green light instead of the high-energy near-UV light that BTZ photocatalysts typically require. The library of photocatalysts was tested using the phosphorylation of quinoline compounds under both batch and recycle flow conditions, achieving up to 40 and 73% conversion, respectively, in 4 h. The versatility of the recycle flow system was further tested by developing a sequential two-step phosphorylation followed by a Minisci coupling procedure using a dual photocatalyst system. This allowed automated production of the target antibacterial phosphorylated quinoline derivative with a total conversion of 64% from abundant, inexpensive, and late-stage modifiable starting materials in a streamlined process.