Metal-free, intermolecular carbopyridylation of alkenes via visible-light-induced reductive radical coupling† †Electronic supplementary information (ESI) available. See DOI: 10.1039/c8sc03493a

An efficient, metal-free strategy for the intermolecular three-component carbopyridylation of styrenes, enabled by Hantzsch ester and visible light, has been described.


S6
A 8 mL vial equipped with a magnetic stir bar was charged with 1, 4-diazabicyclo [2.2.2]octane (DABCO, 0.3 mmol, 1.5 equiv.), HE (0.3 mmol, 1.5 equiv.), cyanopyridines (0.4 mmol, 2.0 equiv.), and Togni reagent (0.3 mmol, 1.5 equiv.). The vial was capped. After evacuated and backfilled nitrogen three times, methyl tert-butyl ether (MTBE) [0.05 M] was added via a syringe, followed by the addition of alkene (0.2 mmol, 1.0 equiv.). The reaction mixture was irritated with a 90 W blue LED, with cooling from a fan. After 24h, the reaction was quenched with H 2 O, extracted with ethyl acetate. The combined organic layers were dried with MgSO 4 , filtered, and concentrated in vacuo. The crude material was purified by flash chromatography to afford the products.

(a) Radical inhibition experiment
The remaining four vials were stirred in the absence of light for an additional 30 min.
Then, one vial was removed for analysis, and the lamps were turned back on to irradiate the remaining three reaction mixtures. After an additional 2 hours of irradiation, the lamps were turned off, and one vial was removed for analysis. The remaining two vials were stirred in the absence of light for an additional 30 min. Then, a vial was removed for analysis, and the lamps were turned back on to irradiate the remaining one reaction mixture. After 4 hours, the lamps were turned off, and the last vial was removed for analysis. The reaction mixtures were analyzed by 19 F NMR with an internal standard. Two standard reaction mixtures in 8 mL vials were charged with DABCO (33.6 mg, 0.3 mmol, 1.5 equiv.), HE (76 mg, 0.3 mmol, 1.5 equiv.), 4-cyanopyridine (41.6 S37 mg, 0.4 mmol, 2.0 equiv.), and Togni reagent (99.0 mg, 0.3 mmol, 1.5 equiv.). The vial was capped. After evacuated and backfilled nitrogen three times, MTBE (4 mL) was added via a syringe, followed by the addition of 4-vinylphenyl acetate (30.6 µL, 0.2 mmol, 1.0 equiv.). The vials were irritated with 90 W blue LEDs. After 2 hour, the lamps were turned off, and one vial was removed from the irradiation setup for analysis.
The last vial was stirred in the absence of light for an additional 16 hours, and then was removed for analysis. The reaction mixtures were analyzed by 19 F NMR with an internal standard.

(a) Absorption and emission spectroscopy
UV-vis spectra were collected on an Agilent Cary 5000 spectrophotometer.
Emission spectra was collected on a Fluorolog-3 spectrofluorometer. All samples were degassed with a stream of argon for 10 minutes, then excited at 375 nm. Figure S3. UV-vis absorption and emission spectra of HE.

(b) Stern-Volmer fluorescence quenching studies
The concentration of HE is 1*10 -5 M. The emission intensity at 442 nm was collected with excited wavelength of 373 nm in DMSO using a Shimadzu RF-5301pc spectrofluorophotometer. After degassing the sample with a stream of argon for 10-15 minutes, plots were constructed according to the Ster-Volmer equation I 0 / I=I + kq t 0 [Q]. Figure S4. HE emission quenching with Togni reagent