Dissolving metals furans

Reductive elimination from 1,2-dibromides generates the alkene in excellent yields. Conformationally rigid, periplanar tro 5-diaxial, also staggered trans-diequatorial, cyclohexane dibromides all afford the alkene at a mercury cathode [110]. In the bicyclo[2,2,2]octane series, the rra s-2,3-dibromide forms the alkene on dissolving metal reduction [111]. The rigid cis-periplanar 1,2 dibromobicy-clo[2,2,l]heptane, at a mercury cathode, also gives the strained alkene which can be trapped as a furan adduct [112]. 

The dissolving metal reduction of benzo[b]furans and dibenzofurans is a classical technique and, depending on the conditions, can give rise to a variety of products.Several examples are summarized in equations (104-108). " The cleavage of dibenzofurans to afford 2-hydroxy biphenyls (equation 107) is a particularly valuable route to these compounds. The reduction of 3-carbomethoxybenzofu-rans with Mg/MeOH (equation 108) is reminiscent of the indole reduction reported earlier (equation 51). 

An organometallic route to muscarine derivatives has been developed (Scheme 1). Reduction of the aa -dibromo-ketone (1) with Fe2(CO)9 in the presence of DMF provided the furanone (2) in good yield. Acetylation of (2) afforded the corresponding enol acetate, which upon Mannich reaction with dimethylamine and formaldehyde gave the furan derivative (3). Deacetylation followed by dissolving-metal reduction and quaternization with methyl iodide gave two isomeric 4-methyl-muscarine salts (4). These compounds showed physiological properties characteristic of the muscarine alkaloids. 

An anionic technique by indirect grafting was proposed for N-metallation of Nylon by Yamaguchi (153-155), in which alcali metals dissolved in liquid ammonia displace the amidic hydrogen atoms. Nylon derivatives and graft copolymers can be synthetized from the N-metallated Nylon (153). For ethylene oxide as grafting monomer, the metallated fibers were soaked in a tetrahydro-furan solution of the monomer, at 60° C (154). Methyl methacrylate is grafted on Nylon with a conversion over 90% by this technique (155). Other procedures involve the use of sodium methoxide in methanol solution and subsequent anionic graft copolymerization of acrylonitrile in a tetrahydrofuran solution (156). 

Two problems occur in using acid hydrolysis for quantitative determinations the occurrence of secondary reactions between some of the compounds released by the hydrolysis (phenols, indoles, furans, etc.) and the dissolution of metals (calcium, aluminum, iron), which subsequently precipitate when the solution pH is neutralized. The latter problem could perhaps be overcome by an initial hydrolysis with water in an autoclave (Stefan and Jocteur-Monrozier, 1983), which would dissolve most of the polysaccharides without dissolving the minerals. 

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