[1488-42-2] · C13H9IO2 · Diphenyliodonium Carboxylate · (MW 324.12)
Alternate Name: (carboxyphenyl)phenyliodonium hydroxide inner salt.
Physical Data: C13H9IO2.H2O: mp 220-222 °C (dec). C13H9IO2: mp 215-216 °C (dec).
Solubility: sol dichloromethane, hot water.
Preparative Method: by oxidation of 2-iodobenzoic acid with potassium persulfate in H2SO4, followed by addition of benzene. It is isolated as colorless prisms of the monohydrate. Anhydrous material can be obtained in quantitative yield by extraction of the monohydrate with dichloromethane and evaporation of the solvent.1
Handling, Storage, and Precautions: described as a stable, easy to handle, safe, crystalline compound.1
Although diphenyliodonium carboxylate is usually represented as an acyclic iodonium salt (1), NMR2 and X-ray diffraction3 studies indicate a cyclic structure (2).
Ullmann-type reaction of diphenyliodonium carboxylate with amines yields anthranilic acid derivatives. Diphenyliodonium carboxylate reacts with anilines in the presence of Copper(II) Acetate to afford the corresponding anthranilic acids (eq 1).4
A protocol for the synthesis of 9-oxoacridan-4-carboxylic acids has also been developed (eq 2).5 This Ullmann-type coupling has been applied to the synthesis of several products of pharmacological interest.6
When a solution of diphenyliodonium carboxylate is heated to 160 °C, decomposition to benzyne, CO2, and iodobenzene takes place (eq 3). This reaction is usually carried out in diglyme (160 °C), although butyrolactone (205 °C) and triglyme (220 °C) have been used in some cases.8
This procedure uses neither basic nor oxidative reagents. The high temperature that is required for decomposition of diphenyliodonium carboxylate leads in some cases to lower yields than alternative procedures, particularly if a thermally unstable reaction partner is used. However, diphenyliodonium carboxylate might be a convenient benzyne precursor for use with substrates of low reactivity; a comparative study of the reactivity of benzyne generated from several precursors (and therefore under a variety of conditions) with the weakly reactive diene thiophene showed that best yields of cycloadduct were obtained using high temperature generation from diphenyliodonium carboxylate.9
Benzyne generated from this precursor has been trapped as a Diels-Alder adduct by several dienes. Trapping efficiency increases in the order anthracene < 1,3-diphenylisobenzofuran < 2,3,4,5-tetraphenylcyclopentadienone (tetracyclone) < 2,5-bis(p-dimethylaminophenyl)-3,4-diphenylcyclopentadienone < 2,5-di-p-anisyl-3,4-diphenylcyclopentadienone.8 When the last of these dienes is used, the adduct is isolated in 79% yield (eq 4).
Benzyne generated by decomposition of diphenyliodonium carboxylate undergoes 1,3-dipolar cycloaddition with pyridinium dicyanomethylide to afford 6-cyanobenz[a]indolizine (eq 5).10
1,4-Diphenyl-1,2,4-triazolium-3-olate does not react with benzyne generated by oxidation of 1-aminobenzotriazole, but if diphenyliodonium carboxylate is used as the benzyne precursor, 2-phenylindazole is obtained by cycloaddition-extrusion reactions (eq 6).11
Disulfides, ditellurides, diselenides, and related compounds undergo insertion of benzyne (eq 7).12,13
Luis Castedo & Enrique Guitián
CSIC & University of Santiago de Compostela, Spain