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

Abstract

[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.

Photoredox Catalysis with Metal Complexes Made from Earth‐Abundant Elements

“…Greany and co-workers found that [Cu(dap) 2 ] + is able to catalyze azide addition to styrene-type double bondsw hen using ah ypervalent iodine reagent (43)a sa na zide source (Scheme 12). [35] In the dark, the lifetime of the resulting benzyl radicali ntermediate is long enought hat another azide radical can add to form bis(azide) products ( 44 b). Upon photoirradiation of [Cu(dap) 2 ] + ,oxidation to the benzylic radical cation presumably takes place, followed by subsequentt rappingw ith methanol (44 a), bromide anions, or other nucleophiles.…”

Iron‐Catalyzed Direct Diazidation for a Broad Range of Olefins

“…[1h] Therefore, searching for a general, yet selective olefin diazidation method has been an important research topic and a range of methods for certain limited types of olefins have been developed. [3] …”

“…However, this method is incompatible with nonstyrenyl olefins. [3a] Fristad and coworkers reported a Mn III -mediated stoichiometric method only for nonfunctionalized aliphatic olefins with a large excess of NaN 3 in acetic acid at 110°C. Snider later reported a key improvement using TFA at −20°C.…”

“…Snider later reported a key improvement using TFA at −20°C. [3b,c] This modified procedure is effective for glycal diazidation, however, it is unsuitable for acyclic aliphatic olefins. The groups of Armimoto and Magnus independently reported (PhIO) n /TMSN 3 -mediated methods specifically for electron-rich allyl silanes and cyclic silyl enol ethers, respectively, at −78°C.…”

“…The groups of Armimoto and Magnus independently reported (PhIO) n /TMSN 3 -mediated methods specifically for electron-rich allyl silanes and cyclic silyl enol ethers, respectively, at −78°C. [3e,f] …”