Metal phenoxides synthesis

Williams225 has recently reported the synthesis of etherimides by treating halogeno- or nitroamides (152) with alkali metal phenoxides (153) in a nonpolar organic solvent in the presence of a phase transfer catalyst. 

G. Sartori, G. Casiraghi, L. Bolzoni, and G. Casnati, General synthesis of 2//-bcnzo fc]pyrans (chrom-3-enes) from metal phenoxides and ,p-unsaturated carbonyl compounds,/. Org. Chem., 44, 803-805 (1979). 

A transition metal catalyzed synthesis of ethers by carbene insertion into the O—bond has been reported. Not only saturated but also unsaturated alcohols can be utilized in this catalytic process. ° Intermolecular and intramolecular oxirane ring opening reactions by alkoxides and phenoxides also provide efficient and stereospecific preparations of acyclic and cyclic ethers. The procedures have been surveyed in detail. ... 

Addition of phenols to activated C—C multiple bonds is another method for O-aUcylation. Conjugated carbonyl compounds with -leaving groups react with metal phenoxides, giving the substituted products via addition-elimination, and the resulted /3-aryloxylated carbonyls are versatile intermediates for synthesis of heterocyclic compounds . Addition... 

Metal phenoxides are utilized extensively in organic synthesis as reagents, since they can readily be prepared from phenols and appropriate metal reagents, and the phenol moiety can easily be modified either sterically or electronically. Particularly, 2,2 -dihydroxy-l,l -binaphthyl (BINOL), salicylideneamine and Af,Af -ethylenebis(salicylideneamine) (salen) proved to be excellent phenol ligands for asymmetric synthesis. Since some of their reactions have recently been reviewed , it may not be appropriate to reproduce all of them. Instead, this section concentrates on the effect of the phenol moiety on the chemical reactivity and selectivity, and tries to provide structure-activity relationships for the metal phenoxide reagents. Metalated derivatives of monophenols, biphenols and salicylaldehyde imines are discussed separately. 

Aromatic hydroxycarboxylic acids, especially salicylic acid, have a wide range of applications, for example, as valuable raw materials and intermediates in the production of pharmaceutical chemicals. Originally, salicylic acid was synthesized by the Kolbe-Schmitt reaction [57], which consists of two steps (1) the synthesis and purification of alkali metal phenoxides and (2) carboxylation (Scheme 4.4). Another possible synthetic method is via the attack of a trichloromethyl cation (generated by a copper catalyst from carbon tetrachloride) on the phenoxide anion, followed by hydrolysis of the C—Cl bonds with concentrated sodium hydroxide, because it is fairly difficult to replace an aromatic hydrogen with carboxyl functionality [58]. 

Although strictly outside the reactions of prenyiphenolic compounds the extensive work on the regiospecific general synthesis of chrom-3-enes (2H-benzo[b]pyrans), in particular2,2-dimethylchromenes, from the reaction of metal phenoxides with 3-methylbut-3-enal is very noteworthy. In the general procedure a solution of titanium tetraethoxide (0.025 mol) in toluene was treated with the phenol (0.1 mol) in toluene and the ethanol formed removed by distillation over... 

The reaction of the carbonato complex with C02 has allowed the demonstration of a facile insertion-deinsertion equilibrium. The study of the deinsertion reaction has allowed estimation of the activation parameters as being = 130 4.0 kJ mor and AS = 121.6 11.9 J moP K . From the above values the authors have calculated an approximate value of the equiUbrium cmistant for the carboxylation reaction equal to 3 x 10 M at 195 K (or a AG value for the same reaction of < 50 kJ moP ), showing that the insertion of CO2 into the M-O-alkyl bond is both kineticaUy and thermodynamically very favored. This trend has also been confirmed for the insertion of CO2 into the Nb-OR bond in [Nb(OR)5]2 (R = methyl, ethyl, aUyl) (see Sect. 6.2.2.1), a catalyst for the synthesis of dialkyl carbonates [67]. Very recently, the facile insertion of CO2 into metal-phenoxide bonds has been reported [68] for cobalt and zinc complexes (Fig. 4.2). It should be noted that such metal systems are used as catalysts in the copolymerization of CO2 with epoxides. 

Alkali metal (haloarylsulfonyl)thio-phenoxides, 364 Alkaline hydrolysis of nylon-6,6, 568-569 of PET, 549-550 Alkyd resins, 18, 30-31, 59-60 synthesis and cure of, 102 Alkylphenolic resins, 376 Alkylphenols, 376, 400 Allophanates, 227... 

Still another possibility in the base-catalyzed reactions of carbonyl compounds is alkylation or similar reaction at the oxygen atom. This is the predominant reaction of phenoxide ion, of course, but for enolates with less resonance stabilization it is exceptional and requires special conditions. Even phenolates react at carbon when the reagent is carbon dioxide, but this may be due merely to the instability of the alternative carbonic half ester. The association of enolate ions with a proton is evidently not very different from the association with metallic cations. Although the equilibrium mixture is about 92 % ketone, the sodium derivative of acetoacetic ester reacts with acetic acid in cold petroleum ether to give the enol. The Perkin ring closure reaction, which depends on C-alkylation, gives the alternative O-alkylation only when it is applied to the synthesis of a four membered ring ... 

The development of metal atom vapor technology over the last 15 years has made available to the chemist a new and useful synthetic technique. A number of novel transition metal compounds have been isolated by the method, particularly in the field of organometallic chemistry. However, the use of vaporized metal atoms for the synthesis of metal alkoxides and phenoxides by condensation into the neat alcohol has been only briefly mentioned in the literature.27... 

The halide derivatives of metals are by far the most useful and widely exploited starting materials for the synthesis of metal alkoxides and phenoxides,1,2... 

The addition of a base, typically ammonia, to mixtures of transition metal halides and alcohols allows the synthesis of homoleptic alkoxides and phenoxides for a wide range of metals. Anhydrous ammonia was first used in the preparation of titanium alkoxides where the reaction is forced to completion by the precipitation of ammonium chloride.41 Although useful for the synthesis of simple alkoxides and phenoxides of Si, Ge, Ti, Zr, Hf, V, Nb, Ta and Fe, as well as a number of lanthanides,42-47 the method fails to produce pure /-butoxides of a number of metals.58 Presumably, secondary reactions between HC1 and Bu OH take place. However, mixing MC14(M = Ti, Zr) with the Bu OH in the presence of pyridine followed by addition of ammonia proves successful, giving excellent yields of the M(OBul)4 complexes.59... 

This method is particularly useful for the synthesis of the alkoxide and phenoxide derivatives of the earlier transition elements. The method is extremely convenient in view of the high volatility of the generated dialkylamines, which are readily removed in vacuum. One major drawback is the synthetic availability of the corresponding metal dialkylamide complex. In some cases the method represents not only the most convenient but also the only synthetic route to an alkoxide derivative. Hence, zirconium tetra-t-butoxide is formed in excellent yield from Zr(NEt2)4 and Bu OH, and the Vlv and CrIV r-butoxides are also readily obtained via this pathway (equation 11).74... 

The carboxylation of phenols is a well established process for synthesis of salicylic acid according to the Kolbe-Schmitt method (Table 4, entry 39). The exothermic reaction is carried out at slightly elevated temperatures around 150 °C and pressures of approximately 5 bar. Batch processes are still mainly used. The main task is to exclude water from the reaction mixture, because this would release the alkali metal hydroxide from the phenoxide salt. 

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