Reagents thallium trifluoroacetate

Oxidation of the tetrahydroisoquinoline (23) by thallium(m) trifluoroacetate in methanol leads to ocoteine (24) in 46% yield. When the same oxidizing reagent, in trifluoroacetic acid, was used in connection with the acetyl amide (25), 7V-acetyl3-methoxynornantenine (26) and the corresponding dehydroaporphine... 

Thallium trifluoroacetate has not enjoyed widespread use as a reagent for quinone synthesis, possibly because it is still a relatively new reagent but more probably because of its toxicity. One example of its use lies in the synthesis of metacyclophanes and related compounds as reported by Tashiro et al Thus the r-butylphenol (59) gave the bisquinone (61), while the phenol (60) afforded the monoquinone (62). An alternative and more practical synthesis of the bisquinone (61) for large scale work involved dealkylation to afford the bisphenol (63) which was then treated with sodium nitrite to give the bisoxime (64). Hydrolysis of the bisoxime did not give the quinone (61), but it could be obtained by zinc/acetic acid reduction of the bisoxime followed by oxidation with nitric acid (Scheme 13). 

Reagents for oxidation 5,5 -dithio-hw-(2-nitrobenzoic acid) (DTNB, Ellman reagent)", silver triflate (AgOTf)", thallium trifluoroacetate (Tl(tfa)3), iodine, and guanidine HCT (Fluka or Sigma-Aldrich). 

Returning to phenol ether-phenol ether coupling, synthetic septicine (59) gave ( )-tylophorine (60) on treatment with thallium trifluoroacetate, and the same reagent converted synthetic julandine (61) to ( )-cryptopleurine (62 69%). In another synthesis of tylophorine the lactam (63) was transformed with va-... 

Lunarine (26), one of the typical neolignans, is biosynthesized by the ortho-para radical coupling between two molecules of p-hydroxycinnamic acid. In this connection, oxidative coupling reactions of 4-substituted phenols have been extensively stndied using thallium trifluoroacetate (TTFA), potassium ferricyanide (K3[Fe(CN)g]) and other reagents. p-Cresol (27) was also electrolyzed at a controlled potential (+0.25 V vi. SCE) in a basic medium to afford Pummerer s ketone 28 in 74% yield. The snggested mechanism is given in Scheme 4. 

Treatment of arylthallium(in) trifluoroacetates with peroxytrifluoroacetic acid has been shown to give relatively good yields of l,4-benzoquinones. " Other synthetic uses for thallium trifluoroacetate species have been described in some detail, and a nice review of thallium-based reagents [including. 

Trifluoroacetates of silver, mercury(II), thallium(lll), lead(IV), and lodme(III) are synthetically valuable reagents that combine the properties of strong electrophiles, oxidizers, and Lewis acids Furthermore, trifluoroacetate anions are stable to oxidation, are weak nucleophiles, and usually do not cause any contamination of the reaction mixture... 

Both the submitters and the checkers used thallium(III) tri-fluoroacetate prepared from thallium(III) oxide and trifluoroacetic acid.3 Although this material may be purchased from Aldrich Chemical Company, Inc. and Eastman Organic Chemicals, the submitters recommend that the reagent be freshly prepared prior to use. 

A simple, high-yield procedure for the conversion of ArTlXj into ArjTlX compounds has recently been described 90). This symmetrization reaction, the mechanism of which is not known, can be effected by treatment of the ArTlX2 compound either with triethyl phosphite or with hot aqueous acetone. As a wide variety of ArTlXj compounds can now be easily prepared by electrophilic thallation of aromatic substrates with thallium(III) trifluoroacetate (q. v.), symmetrization represents the method of choice for the preparation of the majority of ArjTlX compounds. Only about twenty mixed compounds, RR TIX, have been prepared so far, and the only general synthetic procedure available consists of a disproportionation reaction between an RTIX2 species and another organometallic reagent [e.g., Eqs. (5)-(7)]. 

Specifically, it has recently been found 149) that diarylthallium tri-fluoroacetates may be converted into aromatic iodides by refluxing a solution in benzene with an excess of molecular iodine. Yields are excellent (74-94%) and the overall conversion represents, in effect, a procedure for the conversion of aromatic chlorides or bromides into aromatic iodides via intermediate Grignard reagents. The overall stoichiometry for this conversion is represented in Eq. (10), and it would appear that the initial reaction is probably formation of 1 mole of aromatic iodide and 1 mole of arylthallium trifluoroacetate iodide [Eq. (8)] which subsequently spontaneously decomposes to give a second mole of aromatic iodide and thallium(I) trifluoroacetate [Eq. (9)]. Support for this interpretation comes from the... 

Oxidative coupling of aryl tetrahydroisoquinolines. This reagent is superior to thallium(III) trifluoroacetate or vanadium oxyfluoride for nonphenolic oxidative coupling of substrates such as 2 to provide aporphines and homoaporphines (3). 

Biaryl phenol coupling.1 The natural dibenzylbutanolide lignans, prestegane A (la) and B (lb), are converted to the corresponding bisbenzocyclooctadiene lactones (2) by oxidation with Ru02 in TFA-TFAA in 80-85% yield. The usual reagent for this oxidation, thallium tris(trifluoroacetate), is less efficient (45-50% yields). 

In this synthetic approach, thallium(III) trifluoroacetate (see Section 6.1.1.2.2) is employed for the regioselective disulfide generation in the second step. Although the thallium(III) reagent represents a valid alternative to iodine, only a few examples have been reported. 

The enhancement of the electrophilic properties of thallium(III) trifluoroacetate makes it a very important thallation reagent. The products of thallation, eg, arylthallium bis(trifluoracetate), undeigo a variety of substitution reactions, yielding iodides, fluorides, nitriles, thiophenols, phenols, and biaryls. 

The introduction of fluorine into activated arenes is achieved by the combination thallium(III) trifluoroacetate/potassium fluoride/ boron trifluoride. Thallium(III) is hereby an oxidative fluo-rinating reagent.910 Representative compounds prepared in this way are listed below. 

Iodine(III) tnfluoroacetates (iodine tristrifluoroacetate and lodosobenzene bis-trifluoroacetate) resemble lead(IV), thallium(III) and mercury(II) reagents in their reactions but do not share the undesirable high toxicity typical for the heavy metals Iodine tristrifluoroacetate is a very powerful oxidant that can introduce the trifluoroacetoxy group even into alkanes [60 61] Because branched alkanes react ... 

Maritidine. It was observed that a variety of alkoxyl or silyloxy phenols 340 (Scheme 51), on oxidation with the non-toxic pheny 1 iodo-tos-trifluoroacetate, instead of customary heavy metal reagents such as trivalent thallium or pentavalent vanadium salts, in the weakly nucleophilic solvent, trifluoroethanol at low temperature, furnished consistently improved yields of cyclisation products 341 [89],... 

The carboxylates of indium and thallium are obtained by dissolving the oxides in acid. Acetate and trifluoroacetate salts are used extensively as reagents in organic synthesis. Certain other thallium compounds have been used also. The trifluoroacetate, T1(02CCF3)3, will directly thallate aromatic compounds to give arylthal-lium species, for example, C6H5T1(02CCF3)2 (cf. aromatic mercuration, Section 15-15) and oxidize arenes to biaryls. 

---