Flow-Assisted Synthesis of Bicyclic Aziridines via Photochemical Transformation of Pyridinium Salts

Herein is described the development and comparison of homemade continuous-flow reactors, a fluorinated ethylene propylene tube (FEP) reactor (internal diameter of 0.4 cm) and two parallel quartz reactors containing two different internal diameters (0.4 and 0.2 cm), and their application to the photochemical transformation of 1-n-butyl- and 1-allylpyridinium bromide salts (1a and 1b, respectively) to the corresponding α-hydroxycyclopentenoaziridines (6-azabicyclo[3.1.0]­hex-3-en-2-ols) 2a and 2b. Under recirculating conditions, the FEP reactor allowed the production of a greater quantity of bicyclic aziridine (3.2 g), while the quartz reactor with the same diameter furnished the best productivity results (3.7 g L–1 h–1). In addition, the FEP reactor operated efficiently under circulating conditions (1.75 L of 1a) for 4.5 days (residence time of 17.9 h), allowing the production of 2a at a rate of 2 g/day (62–93% conversion).