Metal trifluoroacetates synthesis

The mechanism of the decomposition reaction into metal fluorides has not been elucidated so far. In the first place, metal trifluoroacetates themselves have been relatively less studied among the salts of carboxylic acids. Synthesis and properties of only a few metal trifluoroacetates have been reported (Killings, 1974 Khristov, 1998 Tada, 1999). Thermogravimetry-mass spectrometry (TG-MS) analysis has been carried out to examine the deconposition reaction oflanthanum trifluoroacetate (Eujihara, 2000b). The reaction suggested is... 

Rtlssel C. A pyrolytic route to fluoride glasses. I. Preparation and thermal decomposition of metal trifluoroacetates. J. Non-Cryst. Solids 1993 152 161-166 Rywak A.A., Burlitch J.M. Sol-gel synthesis of nanocrystaUine magnesium fluoride its use in the preparation of Mgp2 films and MgF2-Si02 composites. Chem. Mater. 1996 8 60-67 Saad M., Poulain M. Fluoride glass synthesis by sol-gel process. J. Non-Cryst. Solids 1995 184 352-355... 

The establishment of the stereocenter in efavirenz provides a challenging goal for the synthetic chemist (Pierce et al., 1998 Thompson et al., 1995). The synthesis starts by treating 4-chloroaniline with pivaloyl chloride under biphasic conditions to provide the desired amide 10 (Scheme 6.2). Ortho metallation as directed by the amide is accomplished with two equivalents of n-butyllithium (or w-hexyllithium) in tetramethylethylene diamine (TMEDA) and MTBE. The resulting dianion is quenched with ethyl trifluoroacetate to provide pivaloylamide ketone 11 (Euhrer and Gschwend, 1979). The amide is hydrolyzed in situ to provide the trifluoroketone hydrate hydrochloride 12, which crystallizes from the reaction mixture (>98% pure). 

The ratio of the size of the metal ion and the radius of the internal cavity of the macrocyclic polyether determines the stoichiometry of these complexes. The stoichiometry of these complexes also depends on the coordinating ability of the anion associated with the lanthanide. For example, 12-crown-4 ether forms a bis complex with lanthanide perchlorate in acetonitrile while a 1 1 complex is formed when lanthanide nitrate is used in the synthesis [66]. Unusual stoichiometries of M L are observed when L = 12 crown-4 ether and M is lanthanide trifluoroacetate [67]. In the case of 18-crown-6 ligand and neodymium nitrate a 4 3 stoichiometry has been observed for M L. The composition of the complex [68] has been found to be two units of [Nd(18-crown-6)(N03)]2+ and [Nd(NCh)<--)]3. A similar situation is encountered [69] when L = 2.2.2 cryptand and one has [Eu(N03)5-H20]2- anions and [Eu(2.2.2)N03]+ cations. It is important to note that traces of moisture can lead to polynuclear macrocyclic complexes containing hydroxy lanthanide ions. Thus it is imperative that the synthesis of macrocyclic complexes be performed under anhydrous conditions. 

Hoffman et al. have reported the synthesis of tetrakis-, tris-, and monothiacrown ethers containing a tetra-azaporphyrin unit 139-152. The first porphyradine crown ethers were prepared by the Mgz+ template cyclization of the appropriate crowned derivative of dithiomaleonitrile 32 and 33 to afford 139 and 143, respectively, in ca. 35% yields. Treatment of 139 and 143 with trifluoroacetic acid provided the metal-free porphyrazines 140 and 144, respectively. Subsequent reaction with Ni(OAc)2 or Cu(OAc)2 quantitatively produced 141, 142, 145, and 146 (Scheme 21). 

Whilst carbamate derivatives of indoles and pyrroles are easily prepared, they have limited synthetic utility because they are easily attacked by nucleophiles. For example, A -Aloc525 and A -Cbz526 derivatives of tryptophan are known, but they are destroyed by piperidine. Boc derivatives of indoles, pyrroles and imidazoles are sufficiently hindered to be synthetically useful For example, N-Boc indole is stable towards piperidine and it can be metallated in the 2-position with ferf-butyllithium.527 Nevertheless, they are still more easily cleaved by nucleophiles than Boc-derivatives of secondary amines as illustrated by the fact that Boc-derivatives of pyrrole are cleaved with sodium methoxide, ammonia or hydrazine in methanol527 In tryptophan derivatives, the Ar>w-Boc group is less susceptible to aridolysis than an Na-Boc group with trifluoroacetic acid. However, the M"-Boc group can be cleaved selectively by thermolysis as illustrated by a step in a synthesis of Asperazine [Scheme 8,271 ].52 ... 

An alternative synthesis, suitable for bulky wingtip groups, was introduced by Mercer et al. [53]. The key feature of the synthesis is the reductive dimerisation of a Schiff base by a base metal (manganese, magnesium or zinc) in the presence of trifluoroacetic acid (see Figure 5.13). 

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