Promotion of Sandmeyer hydroxylation (homolytic hydroxydediazoniation) and hydrodediazoniation by chelation of the copper catalyst: bidentate ligandsSandmeyer reactions. Part 8. For part 7 see ref. 1.Electronic supplementary information (ESI) available: EPR evidence for the formation of binuclear complexes by 2-hydroxycarboxylates; reprise of the radical clock results for 2-hydroxycarboxylates. See http://www.rsc.org/suppdata/ob/b4/b404699d/

Abstract

Relative to the rate observed for the hexa-aqua ion, Cu(OH(2))(6)(2+), chelation of the copper catalyst by certain bidentate ligands enhances the rate of hydroxydediazoniation reaction (Sandmeyer hydroxylation); the ligands also provide a source of hydrogen in competitive hydrodediazoniation (H-transfer) reactions. By using the cyclisation of 2-benzoylphenyl radical as a radical clock, it has been possible to evaluate absolute rate constants for both processes effected by a variety of complexes involving one or two bidentate ligands (2-aminocarboxylate, 2-hydroxycarboxylate, 1,3-dicarboxylate, 1,2-diamine). The radical exhibits electrophilic character in both processes. The pattern of behaviour observed suggests the rate determining step in hydroxylation is reaction of the aryl radical at the metal centre to form an organocopper adduct which is rapidly converted into products. The relative reactivities of different complexes are explained qualitatively in terms of variations in the ligand field and Jahn-Teller distortion splittings of the copper d orbitals. Hydrodediazoniation is an S(H)2 H-abstraction process. Generally, coordination by Cu(2+) deactivates the first added ligand relative to its reactivity as a free species in the same state of protonation. For the majority of complexes studied, the relative reactivity as H-donors of 1 : 1 and 1 : 2 complexes is statistically determined but an additional electronic effect is discerned for doubly charged ions.

Synthesis of the Louisianin Alkaloid Family via a 1,2,4-Triazine Inverse-Electron-Demand Diels−Alder Approach

“…Next, an alternative approach to the introduction of the required oxidation at the C-2 position via a hydroxy-Sandmeyer reaction on the 2-pyridyldiazonium salt was explored . Thus, pyridine ester 9 was converted into the 2-aminopyridine 24 , the required diazonium precursor, via a series of straightforward reaction steps; saponification to the potassium carboxylate with potassium trimethylsilanolate, acyl azide formation with diphenylphosphoryl azide, and subsequent Curtius rearrangement followed by acidic deprotection and decarboxylation afforded the desired 2-aminopyridine 24 in a 63% overall yield for this telescoped three-step sequence (Scheme ).…”

Transition-metal-catalyzed synthesis of phenols and aryl thiols

“…In early times, classic methods for the synthesis of phenols included the sulfonation of benzene [11], the Dakin reaction [12–13] and the Sandmeyer-type reaction [14]. These methods are useful for the preparation of various phenols, however, they suffer from several drawbacks such as multistep syntheses, toxic solvents, high temperatures, a narrow substrate scope, low selectivity, and/or low yields.…”

Recent trends in the chemistry of Sandmeyer reaction: a review

“…They are frequently used for the preparation of organic nanocompounds and grafted a variety of organic molecules on metallic surfaces [2]. Furthermore, Meerwein arylation [3,4], Balz-Schiemann [5,6] and various metal-catalyzed reactions [7,8] involve diazonium salts as starting precursors for the production of various halides, phenols, cyanides, azides and alkenes [9] which serve as effective intermediates for the synthesis of important molecules [10][11][12][13]. Sandmeyer reaction is one of them, in which diazonium salts are used for the construction of carbon-halogen, carbon-phosphorous, carbon-sulfur, carbon-selenium, carbon-boron bond formation.…”