Sandmeyer reactions. Part 7.1 An investigation into the reduction steps of Sandmeyer hydroxylation and chlorination reactions

Reactivity of 3‐Methylbenzenediazonium Ions with Gallic Acid. Kinetics and Mechanism of the Reaction

“…Investigations by Broxton and Roper [40] confirmed that the initial reaction of the arenediazonium ions takes place in such a way that the (Z)-diazo ether is formed directly almost exclusively, and part of it is then transformed to the thermodynamically more stable (E)-isomer (which can in some instances be isolated) [20] by an ionization -recombination mechanism (Broxton and Roper [40]) or by a bond-rotating mechanism that has been described for Sandmeyer hydroxylations and chlorination reactions [41] but has not been extended to other systems.…”

pH Effects on Ethanolysis of Some Arenediazonium Ions: Evidence for Homolytic Dediazoniation Proceeding through Formation of Transient Diazo Ethers

“…Investigations developed by Broxton et al [36] confirmed that the initial reaction of the arenediazonium ions takes place in such a way that the (Z)-diazo ether is directly formed almost exclusively, and part of it is transformed to the (E) isomer by an ionization-recombination mechanism. [3,19] Given that almost quantitative yields of the reduction product ArH are obtained at pH Ͼ 6, it is likely that the initially formed (Z)-diazo ether undergoes homolytic fragmentation to give EtO · and the arenediazenyl radical ArN 2 · , which immediately decomposes to yield the aryl radical Ar · and N 2 . Once the radicals are formed, an H · atom from EtO · is abstracted, giving rise to the ArH derivative.…”

“…These (Z) adducts may undergo subsequent isomerization to the thermodynamically more stable (E) isomers, which in some instances can be isolated, [18] or may eventually give rise to homolytic rupture of the bonds providing the initiation of a radical process. [3,9,19,20] This bond-rotating mechanism to transform the (Z) into the (E) isomers has recently been described for Sandmeyer hydroxylations and chlorination reactions. [19] In most instances analyzed, the nucleophile must possess a charge, such as OH Ϫ , CN Ϫ , RO Ϫ or ascorbate ions, and experimental conditions are chosen such that substantial concentrations of the anionic form of the nucleophile are present, [3,9,19,20] but formation of (Z)-diazo ethers with neutral nucleophiles has also been reported.…”

“…[3,9,19,20] This bond-rotating mechanism to transform the (Z) into the (E) isomers has recently been described for Sandmeyer hydroxylations and chlorination reactions. [19] In most instances analyzed, the nucleophile must possess a charge, such as OH Ϫ , CN Ϫ , RO Ϫ or ascorbate ions, and experimental conditions are chosen such that substantial concentrations of the anionic form of the nucleophile are present, [3,9,19,20] but formation of (Z)-diazo ethers with neutral nucleophiles has also been reported. [5,21] Following previous solvolytic work, [5,26] we have undertaken a study to investigate the effects of pH (0Ϫ7) on the ethanolysis of 2-, 3-and 4-methylbenzcenediazonium ions (2MBD, 3MBD, and 4MBD, respectively) by a combination of spectrophotometric (UV/Vis) and chromatographic (HPLC) techniques to seek for evidence of the nature of the initiation step in solvolytic radical dediazoniations.…”

Synthesis of Substituted Phenols by Using the Ring‐Closing Metathesis/Isoaromatization Approach

“…[21] 2-Bromo-3-indol-1-yl-propene was prepared by alkylation of indole with 2,3-dibromopropene according to the reported procedure. [22] 5-Hexenal, [23] 4-cyclohexyl-3-phenyl-5-hexenol, [24] (E)-3-allyl-2-iodocyclononene (8 f), [25] activated MnO 2 , [26] Dess-Martin periodinane, [27] and p-methoxybenzenediazonium tetrafluoroborate (12) [28] were prepared according to the reported procedures. a-Bromostyrene, 2,3-dibromopropene, indole, tert-butyllithium solution, vinylmagnesium chloride solution, DBU, palladium diacetate, rhodium trichloride, and cesium carbonate were used as received.…”