An increasingly sustainable photochemical synthesis of carbazoles was developed using a catalytic system of Fe(phen)(NTf)/O under continuous flow conditions and was demonstrated on gram-scale using a numbering-up strategy. Photocyclization of triaryl and diarylamines into the corresponding carbazoles occurs in general in higher yields than with previously developed photocatalysts.
Polycyclic heterocycles can be formed in good to excellent yields via photochemical conversion of the corresponding substituted aryl azides under irradiation with purple LEDs in a continuous flow reactor.
The synthesis and derivatization of carbazoles based upon the natural product clausine C has been accomplished using two different two‐step continuous processes. The resulting carbazoles (9 examples, 33–74 % yield) were prepared by means of a continuous flow set‐up integrating a UV‐mediated transformation employing a purple LED reactor (λ=394 nm) as the first step in the multi‐step sequence. The second derivatization step involved cross‐coupling through Pd‐catalyzed Suzuki cross‐coupling or Ni‐catalyzed metallophotoredox cross‐coupling with potassium trifluoroborate salts. The latter represents the first example of using sequential photochemical reactors, at different wavelengths, in a continuous flow process.
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