Metal procedures

Transfer of the acyl group from the acylzirconocene chloride to aluminum (transmetala-tion) by treatment with aluminum chloride has been reported to give an acylaluminum species in situ, and the possibility of the acylaluminum acting as an acyl anion donor has been suggested (Scheme 5.5) [7]. However, the acyl anion chemistry through this trans-metalation procedure appears to be limited since only protonolysis to the aldehyde proceeds in good yield, which could be achieved by direct hydrolysis of the acylzirconocene chloride. 

After completion of this chapter, Snieckus et al. published examples of the solid-phase Stille105 and Suzuki106 reactions in which were included stannanes and boronic acids synthesized in solution via a directed ortho metalation procedure,107 ultimately allowing for the construction of a range of tricyclic structures. 

An intermediate of the metallation procedure, the adduct cis-PtCl2H2-(Hemato-XI), has been characterized [86c]. Tetrabenzporphyrin was transformed into its Pd and Pt complexes, Pd(TBP) or Pt(TBP), with PdCl2 in DMF [87]. 

Alternatively, reaction of 7 with the appropriate metal salt in the presence of base and air gives the stable aromatic (sp2) texaphyrin metal complex 9 in a one-step oxidation and metalation procedure [6,7,20,26-28],... 

The formation of an alkanethiolate SAM on Au has been used to direct subsequent metallization procedures.62 In this way, a smooth junction between adjacent Ni and Au metal layers was formed on the surface of the Si02. 

Regioselective substitution reactions of a series of 2- and 3-hydroxybiaryls including BINOL have been performed via a new directed orf/io-metallation procedure.75 O-Aryl AMsopropylcarbamates, conveniently prepared from phenols and isopropyl isocyanate, have been temporarily and in situ N-protected by means of silyl inflates to form stable intermediates for low-temperature lithiation reactions using n-BuLi-TMEDA in diethyl ether. The IV,IV-dialkyl aryl O-sulfamate has been reported as a new directed metallation group.76... 

An intermolecular version of the arylation of carbamates has been recently published by Hartwig et al. (Eq. (21)) [132]. His group showed that reactions catalyzed by a combination of Pd(OAc)2 and P( -Bu)3 formed /V-aryl carbamates from aryl bromides or chlorides and f-butylcarbamate as substrate. Again, the reaction conditions were not as mild as those for amination, but were similar to those of the intramolecular reactions. For the intermolecular reactions, the use of sodium phenox-ide as base was crucial. Reactions using Cs2C03 showed low conversions. Those involving NaO-r-Bu as base rapidly formed a gel, presumably from the deproto-nated carbamate, and also showed little or no conversion. The products of these reactions serve as conveniently protected anilines, and r-butylcarbamate can be considered one type of ammonia surrogate. In addition, the products of these reactions are suitable for subsequent directed metalation procedures [100]. 

Anionic graft-polymerization of paraformaldehyde onto starch and dextrin has been effected in methyl sulfoxide solution, polymerization being initiated by the carbohydrate potassium alcoholate formed from the reaction of the carbohydrate with naphthalene potassium, a metallation procedure not previously described for carbohydrates.220... 

Usually decarboxylation is accomplished by heating the acids above their melting points, often in the presence of a copper-chromium catalyst. Imidazole-4,5-dicarboxylic acid can be monodecarboxylated by heating its monoanilide imidazole- and benzimidazole-2-carboxylic acids decarboxylate very readily indeed, so readily that the carboxyl function makes a useful blocking group in metallation procedures (see Scheme 7.2.1) [3-5]. A potentially useful method of preparation of imidazole-4-carboxylic acid derivatives heats the 4,5-dicarboxylic acid (2) with acetic anhydride to form (1), which is essentially an azolide and very prone to nucleophilic attack which cleaves the nitrogen-carbonyl bond (Scheme 8.3.1). With methanol the methyl ester (3) is formed with hydrazines the 4-hydrazides (4) result [6]. 

These reagents open the oxirane ring at the sterically more hindered side, and the reductions are accompanied by retention of the configuration. The alkali metal procedures can be employed as a comparatively simple and clean method of reducing sterically hindered oxiranes. A general synthetic method has been developed with this procedure for the preparation of 2-ethynylcycloalkanols. ... 

In a chip-fabrication process, the substrate may undergo two or three deposition processes, 20 patterning processes, 10 etching procedures and further ion implantation and metallization procedures. 

Goldberg and Bailey (44) have used the asymmetric-directed metalation procedure as a route to compounds demonstrating (for the first time) pseudoasymmetry in ferrocenes. A pseudoasymmetric 1,2-disubsti-tuted ferrocene was prepared by procedures such as those illustrated in Figure 1. 

One of the most useful synthetic applications of the directed metalation reactions is in preparing heterocyclic systems. Of the available directing groups, those involving N-chelated intermediates have been by far the most useful. In several instances the route provided by ortho lithiation constitutes the only available method for preparing certain heterocycles. In other cases such syntheses, although not the only routes available, represent a considerable improvement over more conventional methods, especially considering the number of steps in the overall synthesis and yields. Furthermore many of the heterocyclic compounds produced via directed metalation procedures are of extreme interest in that they are natural products or derivatives thereof. 

Narasimhan and Ranade (57) have incorporated the 2-metalation procedure into the preparation of isoquinoline. Furthermore their obser-... 

Narasimhan and Bhide (59) have also devised an elegant route for transforming laudanosine to tetrahydropalmitine via a directed metalation procedure (Reaction 45). This reaction sequence is important because there was previously no synthetic route for this transformation. 

Introducing the fluorine atom via an electrophilic fluorination reagent requires a two-stage bromination and low-temperature metalation procedure that is followed by a chromatographic purification. 

The parent hydrocarbons benzene and naphthalene have a poor kinetic acidity and attempts at metallation using alkyllithium in THF or Et20 result only in attack on the solvent. Quantitative conversion into phenyllithium can be effected however, if a large excess of benzene is allowed to react with BuLi TMEDA in hexane at reflux temperature [9, 167]. In the case of naphthalene this metallation procedure has no practical importance, because 1- and 2-naphthyllithium are produced in comparable amounts, along with some dimetallated naphthalene ([9], compare also [160]). 

The reduction-aeration (often with included pre-concentration on noble metals) procedures are easy to perform, rapid, selective, and accurate by comparison with many other techniques, and thus are still almost exclusively used particularly in routine toxicological and environmental analysis (Schaller 1985, 2003, Ewers 2003, Welz and Sperling 1999, pp. 675-676). 

Cluster and Cage Compounds Containing Transition Metals Procedure... 

Certain grades of commercial zinc are quite pure. The highest purity may be achieved by distillation (Procedure I) or, starting from ZnS04, by purification of the salt and electrolytic isolation of the metal (Procedures 1 and II). Extreme purity of zinc salts is particularly important in the preparation of scintillators. 

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