Recent developments in photochemical reactions of diazo compounds

Abstract

Chemistry of diazo compounds is dominated by transition metal catalysis but recently, photoinitiated reactions of diazo compounds have attracted a lot of attention. This mini-review describes recent discoveries on the reactivity of diazo compounds under light irradiation.

Photoinduced Proton Transfer Reactions for Mild O-H Functionalization Reactions of Unreactive Alcohols

“…The least acidic iPrOH showed only a very minor chemical shift perturbation of 0.03 ppm (Table 2). Importantly, a similar trend was observed in 13 C-NMR of the ester carbonyl and methyl group (Table 2). All samples did not undergo a spontaneous O-H functionalization reaction of the alcohol in the dark.…”

“…[12] It would harness HFIP as a reagent in organic synthesis and allow the direct introduction of hexafluoro isopropyl ether groups into organic molecules. We thus commenced our studies by investigating the reaction of HFIP with phenyl diazoacetate 6a under photochemical conditions [13] and were delighted to observe that the functionalization of HFIP readily occurred within 4 hours reaction time at ambient temperature in excellent yield and without the need of further purification ( Table 1, entry 1). We could subsequently reduce the amount of HFIP to 1.0 equivalent and obtained the desired product 10a as an analytically pure sample after simple evaporation of solvent ( Table 1, entry 2-4).…”

Blue Light‐Promoted N−H Insertion of Carbazoles, Pyrazoles and 1,2,3‐Triazoles into Aryldiazoacetates

“…Upon irradiation in the blue/ violet region of the visible spectrum, the photoexcited diazo compound liberates N 2 , thus generating a highly reactive carbene intermediate, which can be trapped with several reacting partners. [4] Examples of cyclopropanations with styrene and arenes; and XÀ H insertions (X=C, N, O) involving carboxylic acids, amines, alkanes and arenes have been reported; [5,6] they have been also reacted with ethyl diazoacetate to afford trisubstituted olefins; [7] underwent cyclopropenation reaction with alkynes; [8] sigmatropic shifts involving sulfur ylides; [8,9] cyclopropenations with hindered propargyl alcohols; [10] or cyclopropanations with indoles. [11] In this context, and as an alternative to metal catalyzed processes, we became also interested in the possibility of developing blue light-promoted NÀ H insertion protocols of carbazoles, pyrazoles and 1,2,3triazoles into aryldiazoacetates.…”

Room Temperature Coupling of Aryldiazoacetates with Boronic Acids Enhanced by Blue Light Irradiation

“…Photochemical reactions employing diazo compounds and UV light have been extensively studied in the past century . However, it was only recently that the visible‐light photochemistry of these compounds started to be more intensively investigated by using some of their donor–acceptor congeners, aryldiazoacetates …”