Halo ethers, reaction with metallates

By reaction of an a-halo ester 1 with zinc metal in an inert solvent such as diethyl ether, tetrahydrofuran or dioxane, an organozinc compound 2 is formed (a Grignard reagent-like species). Some of these organozinc compounds are quite stable even a structure elucidation by x-ray analysis is possible in certain cases ... 

Ketene di(2-melhoxyethyl) acetal has been obtained by the present method with the use of diethylene glycol dimethyl ether as solvent.3 Other methods for the preparation of ketene acetals include the dehydrohalogenation of a halo acetal with potassium t-butoxide 4 and the reaction of an a-bromo orthoester with metallic sodium.5... 

This procedure illustrates a general method for the stereoselective synthesis of ( P)-disubstitnted alkenyl alcohols. The reductive elimination of cyclic /3-halo-ethers with metals was first introduced by Paul3 and one example, the conversion of tetrahydrofurfuryl chloride [2-(chloromethyl)tetrahydrofuran] to 4-penten-l-ol, is described in an earlier volume of this series.4 In 1947 Paul and Riobe5 prepared 4-nonen-l-ol by this method, and the general method has subsequently been applied to obtain alkenyl alcohols with other substitution patterns.2,6-8 (I )-4-Hexen-l-ol has been prepared by this method9 and in lower yield by an analogous reaction with 3-bromo-2-methyltetra-hydropyran.10... 

Reaction of Metallated Acetylenes with Alkyl Halides, a-Halo-ethers, Epoxides and Alkyl Orthoformates... 

The catalyzed reaction of enol ethers with carbonyl compounds (Scheme 1) has become an important reaction in synthesis. Compared to the metal enolate reactions (Part 1, Volume 2), the catalyz enol ether reactions offer the following distinct differences. Enol ethers are often isolable, stable covalent compounds, whereas the metal enolates are usually generated and used in situ. Under Lewis acid catalyzed conditions, a number of functional equivalents such as acetals, orthoesters, thioacetals, a-halo ethers and sulfides can participate as the electrophilic components, whereas many of them are normally unreactive towards metal enolates. In synthesis, enol ether reactions now rival and complement the enolate reactions in usefulness. Enol silyl ethers are particularly useful because of their ease of preparation, their reasonable reactivity and the mildness of the desilylation process. 

As the accompanying equations illustrate, the reactions of enol silyl ethers are regarded as those of either electron-rich olefins or stable metal enolates. The treatments of eno/ silyl ethers with halogens, NBS, sulfenyl halides, and nitronium ions afford the corresponding a-halo, alkylthio, and nitro ketones, respectively (eq (22)) [19]. 

Many routes to 0x0 and imido compounds have been developed. Transition metal-oxo complexes are coimnonplace and, in many cases, are the most stable form of an element in air. Some imido compoimds, including the first imido complex, have been prepared from metal-oxo complexes (Equation 13.50). The reactions of some of the later metal-oxo compounds with a primary amine generate an imido species by extrusion of water. In other cases, metal-imido complexes are prepared from 0x0 complexes by the reaction of phosphmimines (Equation 13.51) or from 0x0 or halo complexes by the reactions of silylamines (Equations 13.52 and 13.53). The driving force for these reactions is the formation of phosphine oxide, silyl ethers, or silyl halides. 

Examples of the coupling of aryl iodides and bromides with phenols in the presence of catalytic amounts of copper are shown in Equations 19.107-19.113. The reactions of aryl iodides and bromides with a variety of phenols occur in the presence of (CuOTf), PhH as catalyst and CSjCOj as base (Equation 19.107). The air-stable [Cu(MeCN)JPF (5 mol %) also was shown to catalyze the formation of biaryl ethers. As shown in Equation 19.108, o-halo tertiary and secondary benzamides and.sulfonamides that were prepared by ortho-metallation procedures were suitable coupling partners. ... 

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