[563-68-8] · C2H3O2Tl · Thallium(I) Acetate · (MW 263.43)
Physical Data: mp 110 °C; d 3.68 g cm-3.
Solubility: sol water, alcohol, acetic acid.
Form Supplied in: silk-white crystals; widely available.
Handling, Storage, and Precautions: thallium reagents are extremely toxic. The reactions should be carried out in a well-ventilated fume hood, and rubber gloves should be worn. Thallium(I) acetate is reported as a human poison by unspecified routes.4
As an inexpensive and stable substitute for Silver(I) Acetate, TlIOAc reacts with stoichiometric amounts of alkenes and Iodine in acetic acid to produce trans-a-iodoacetates in high yields (eq 1).1 The reaction can be carried out in a nonhomogeneous system using benzene or CH2Cl2 as a solvent, where more than two equiv of the thallium salt are required. This reaction is not highly regioselective for trisubstituted alkenes,5,6 and no addition was observed for electron-poor alkenes such as methyl cinnamate.7 When enol acetates are used as alkenes, the corresponding a-iodo ketones are formed (eq 2).8 This reaction is a mild alternative to the N-Iodosuccinimide procedure for a-iodination of ketones.
Thallium acetate can be used in the Prevost reaction9 (
dry) and in the Woodward modification10 (
wet) for stereoselective vicinal diol formation. trans-1,2-Diacetoxycyclohexane is obtained when a mixture of TlOAc, I2, and cyclohexene (a stoichiometric ratio of 2:1:1) is heated at reflux in anhydrous acetic acid.2 After hydrolysis of the acetyl groups, trans-1,2-cyclohexanediol is obtained in 65-70% yields (eq 3). In the Woodward modification the reaction mixture is heated at reflux in aqueous acetic acid to afford cis-hydroxyacetate, which, upon hydrolysis, produces cis-1,2-cyclohexanediol in 70-75% yields (eq 4).2
Intramolecular iodocarboxylation of unsaturated carboxylic acids in the presence of a stoichiometric amount of TlOAc in CH2Cl2 leads to iodolactones in high yields (eq 5).3 The kinetically controlled product is formed under neutral and nonaqueous conditions.
TlOAc catalyzes the formation of isothiocyanates from isocyanides and disulfides (eq 6).11 Various isocyanides can be used in this reaction, and the best yields are obtained with dibenzoyl disulfide. The reactions are carried out at 61-85 °C in various solvents such as CHCl3, toluene, cyclohexane, EtOH, and dioxane. TlOAc also catalyzes rearrangements of ten-membered-ring allenes to tricyclic compounds in acetic acid at room temperature (eq 7).12 The double bond at C-5-C-6 is required for the rearrangement to occur.
TlOAc promotes palladium-catalyzed intramolecular cyclization-carbonylation of properly substituted aromatic iodides (eq 8).13 When Triethylamine is used as the base instead of TlOAc, a low yield of cyclization-carbonylation product is obtained, which is accompanied by the product derived from the direct carbonylation process. Besides the above examples, bromination of benzene or toluene and selective ortho-iodination of phenols mediated by TlOAc were reported.14,7
Myong Ji University, Seoul, Korea