Alkylsilber- und Alkylgold-Reagenzien, II. Cyano(methyl)argentate: Spektroskopie, Selektivität als Methylierungsreagenzien, Vergleich mit anderen Methylsilber-Reagenzien

As the first examples of a new type of Ag complex the cyanoargentates MeAg(CN)Li (1), Me2Ag(CN)Li2 (2), MeAg(CN)MgBr (3), and Me2Ag(CN)(MgBr)2 (4) were prepared in solution or suspension by transmetallation of MeLi or MeMgBr with AgCN. Compared to AgBr-derived reagents, such as MeAg . MgBr2 (5) and Me2AgMgBr (6), the cyano(methyl)argentates argentates are clearly less sensitive to light. According to the IR spectrum, the Ag atom of 2 is connected with the cyano group. The C-13-NMR spectra of 2, 4, 5, and 6 furnish proof of the Ag - Me group in these compounds and points to the partial structure Ag - Me - Mg in 4, 5, and 6. - Complexes 2 (stable up to 20-degrees-C), 4, 5, and 6 methylate the ketoaldehyde 13 with high selectivity at the aldehyde group (best yield with 4). 4, 5, and 6 exhibit high cheleselectivity in the reaction with the hydroxy diketone 22 (best yield with 4) and comparable intermolecular competitive systems. 2 and 6 methylate 11,12-epoxy-2-deodecanone (28) with virtually complete regioselective ring opening to give 11-hydroxy-2-tridecanone (29). In contrast to Me2Cu(CN)Li2 (7) and Me2CuMgBr, the analogous reagents Me2Ag(CN)Li2 (2) and Me2AgMgBr (6) methylate styrene oxide (32), and 6 also methylates alpha-methylstyrene oxide (36) in alpha-position to the phenyl residue with high selectivity, yielding nearly exclusively 2-phenylpropanol (33) or 2-methyl-2-phenylpropanol (37), respectively. The selective "alpha attack" of Ag reagents is explained by fixation of the reagent to the phenyl residue of 32 and 36 in the first reaction step.