Developments in the Photochemistry of Diazo Compounds

Abstract

This review focus on photolytic reactions of diazo compounds, covering mainly synthetic applications such as Wolff rearrangement, 1,2-shift, X-H insertion, cyclopropanation, hydrogen abstraction and reaction with oxygen and physical organic studies, with special relevance to mechanistic considerations. the synthesis of a diazo compound if loss of a proton from the C()-atom of the primarily formed alkanediazonium ion is faster than the loss of dinitrogen, which makes this method almost specific for the case of aliphatic amines containing a C()-atom substituted by an acidifying group. Diazo compounds can also be prepared by acylation or cleavage of aliphatic diazo compounds containing the structural requirements. For instance, diazo carbonyl carbamate 4 can be prepared through the reaction of the carboxylate precursor with a chloroformate and further reaction of the anhydride with diazomethane (Scheme 2).[13] Making use of oxidants, diazo carbonyl compounds can be prepared by hydrazone oxidation in the presence of mercury oxide and potassium hydroxide.[14] Scheme 1 Scheme 2 Diazo-transfer reactions have been widely used since they are a more general method for the preparation of diazo compounds. In this reaction, the diazo moiety is transferred from the donor to an acceptor where the donor is a sulphonyl azide (6) and the acceptor a carbanion formed after deprotonation (Scheme 3).[3,15] Scheme 3 Diazo compounds can be submitted to several reaction conditions and myriads of compounds can be obtained by the proper choice of conditions and reagents. In the absence of a metal catalyst, this decomposition can be induced by thermolysis or photolysis, generating a highly reactive intermediate species that, in most cases, affords a complex mixture of products. Depending on the diazo compound and the reaction conditions, the resulting products can be derived from C-H or X-H

2-Diazo-1-(4-hydroxyphenyl)ethanone: a versatile photochemical and synthetic reagent

“…When samples were purged for 30 min either with argon or with 100% O 2 before photolysis, the Stern-Volmer dependence on the quencher concentration was used to determine the triplet lifetime (τ= 1.5 × 10 −10 s) and the rate of appearance of 4a of 6.6 × 10 9 s −1 using an estimated rate constant for O 2 diffusion of k diff = 1.37 × 10 10 M −1 s −1 in 50% aqueous acetonitrile (Table 4 and Figure SI5). 24,45,46,47,48 …”

Recent Developments in Azide‐Free Synthesis of 1,2,3‐Triazoles

“…Diazo compounds have also found extensive applications in organic synthesis as reactive carbene precursors upon dediazonization under thermolytic or photolytic conditions. [76][77][78][79][80][81][82] Furthermore, diazo compounds could be applied into the construction of various nitrogen-containing heterocycles, such as 1,2,3-triazoles, with the retention of two nitrogen atoms.…”

Into the Blue: Ketene Multicomponent Reactions under Visible Light

“…Modern chemistry of diazo compounds is dominated by transition metal catalysis, although photoinduced and thermal decompositions have also found application. 1 Photoinitiated reactions have experienced a revival of interest due to the increased understanding of photochemical mechanisms. The photoinitiated decomposition of diazocompounds is mainly induced by UV irradiation, and only recently the use of visible light has been reported by some authors.…”