Three-Component Azidation of Styrene-Type Double Bonds: Light-Switchable Behavior of a Copper Photoredox Catalyst**

[Cu(dap)2]Cl effectively catalyzes azide addition from the Zhdankin reagent to styrene-type double bonds, and subsequent addition of a third component to the benzylic position. In the presence of light, a photoredox cycle is implicated with polar components such as methanol or bromide adding to a benzylic cation. In the absence of light, by contrast, double azidation takes place to give diazides. Therefore, regioselective double functionalization can be achieved in good to excellent yields, with a switch between light and dark controlling the degree of azidation.

Infrared spectra were recorded on a spectrometer as neat using a Perkin-Elmer FT-IR Spectrum RX1 or BX spectrometers.
LCMS analysis was performed on a Agilent 1200 series fitted with a 3.0 x 20 mm, C18, 3.0 m column, with a single quadrupole Agilent 6100 mass spectrometrer, with ESI ionisation. Elution was carried out using reverse phase gradient of MeOH-water with 0.1% formic acid.
Low resolution mass spectrometry was performed on an Agilent 6100 mass spectrometer (ESI ionisation) and Hewlett Packard 5971 MSD (GC/MS with EI). High resolution mass spectrometry was performed on a Waters QTOF with ESI/APCI ionisation and a Thermo Finnigan MAT95XP (EI).
Melting points were determined using a Kofler hot-stage apparatus or Stuart Scientific SMP10 apparatus and are uncorrected. Thin layer chromatography (TLC) was performed using pre-coated Merck 60F254 silica plates. Visualization was performed using either UV light or treatment with acidic potassium permanganate. Flash chromatography was performed using Merck Kieselgel (mesh size 220-240) silica.
All reagents and solvents were used as obtained from commercial source, unless otherwise stated. Solvents were degassed by bubbling nitrogen gas through them for twenty minutes prior to use.

Safety:
Azides are potentially explosive compounds and require appropriate safety protocols to be observed at all times. 6 N.B.  [1,2]iodaoxol-3(1H)-one, 1, is more stable than other iodine azide reagents, it is reported to decompose with explosion at 138-139°C. 7 In the course of reaction optimisation for this work, we observed an explosive decomposition of reagent 1 (100 mg, (s)) in the presence of excess KSCN (s) in a vial at room temperature.
A vial containing Cu(dap) 2 Cl (4.4 mg, 5 mol, 0.01 eq), 1,2-diazidoethylbenzene (X mg, X mmol, 1 eq) and equipped with a stirrer bar, sealed with a septum, was purged under a flux of nitrogen. Then degassed methanol (5 mL) and styrene (290 L, 2.5 mmol, 5 eq) were added and the tube was sealed and put 1 cm away from a 30 W fluorescent bulb and stirred for 18 hours. The reaction mixture was loaded on silica and purified by flash column chromatography eluting with a mixture hexane:ethyl acetate = 100:0 to 98:2.

C) TEMPO control reaction
A vial containing Cu(dap) 2 Cl (4.4 mg, 5 mol, 0.01 eq), 1-azido-1 3 -benzo[d] [1,2]iodaoxol-3(1H)one (145 mg, 0.5 mmol, 1 eq) and equipped with a stirrer bar, sealed with a septum, was purged under a flux of nitrogen. Then a solution of TEMPO (156 mg, 1 mmol, 2 eq) in degassed methanol (5 mL) and styrene (290 L, 2.5 mmol, 5 eq) were added and the tube was sealed and put 1 cm away from a 30 W fluorescent bulb and stirred for 18 hours. S8 [1,2]iodaoxol-3(1H)one (145 mg, 0.5 mmol, 1 eq) and equipped with a stirrer bar, sealed with a septum, was purged under a flux of nitrogen. Then degassed methanol (5 mL) and styrene (290 L, 2.5 mmol, 5 eq) were added and the tube was sealed and put 1 cm away from a 30 W fluorescent bulb and stirred for a certain number of hours. The reaction mixture was loaded on silica and purified by flash column chromatography eluting with a mixture hexane:ethyl acetate = 100:0 to 95:5.

Typical procedures for the three component azido-functionalisation of styrenes
General procedure A A vial containing Cu(dap) 2 Cl (4.4 mg, 5 mol, 0.01 eq), 1-azido-1 3 -benzo[d] [1,2]iodaoxol-3(1H)one (145 mg, 0.5 mmol, 1 eq) and equipped with a stirrer bar, sealed with a septum, was purged under a flux of nitrogen. Then degassed methanol (5 mL) and the styrene (2.5 mmol, 5 eq) were added and the tube was sealed and put 1 cm away from a 30 W fluorescent bulb and stirred for 18 hours. The reaction mixture was loaded on silica and purified by flash column chromatography eluting with a mixture hexane:ethyl acetate = 100:0 to 95:5.
General procedure B (for the trapping of different solvents) A vial containing Cu(dap) 2 Cl (4.4 mg, 5 mol, 0.01 eq), 1-azido-1 3 -benzo[d] [1,2]iodaoxol-3(1H)one (145 mg, 0.5 mmol, 1 eq) and equipped with a stirrer bar, sealed with a septum, was purged under a flux of nitrogen. Then degassed solvent (5 mL) and the styrene (2.5 mmol, 5 eq) were added and the tube was sealed and put 1 cm away from a 30 W fluorescent bulb and stirred for 18 hours. The reaction mixture was loaded on silica and purified by flash column chromatography eluting with a mixture hexane:ethyl acetate = 100:0 to 95:5.

General procedure D (for the diazidation)
A vial containing Cu(dap) 2 Cl (4.4 mg, 5 mol, 0.01 eq), 1-azido-1 3 -benzo[d] [1,2]iodaoxol-3(1H)one (145 mg, 0.5 mmol, 1 eq) and equipped with a stirrer bar, sealed with a septum, was covered in aluminium foil and purged under a flux of nitrogen. Then degassed methanol (5 mL) and the styrene (2.5 mmol, 5 eq) were added and the tube was sealed the reaction mixture stirred for 18 hours in the dark. The reaction mixture was loaded on silica and purified by flash column chromatography eluting with a mixture hexane:ethyl acetate = 100:0 to 98:2. S11