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

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Abstract
Alkylsilver and Alkylgold Reagents, II[1]. – Cyano(methyl)argentates: Spectroscopy, Selectivity as Methylating Reagents, Comparison with Other Methylsilver ReagentsAs 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 are clearly less sensitive to light. According to the IR spectrum, the Ag atom of2is connected with the cyano group. The13C‐NMR spectra of2, 4, 5, and6furnish proof of the Ag – Me group in these compounds and points to the partial structure Ag – Me – Mg in4, 5, and6. – Complexes2(stable up to 20°C),4, 5, and6methylate the ketoaldehyde13with high selectivity at the aldehyde group (best yield with4). 4, 5, and6exhibit high cheleselectivity in the reaction with the hydroxy diketone22(best yield with4) and comparable intermolecular competitive systems.2and6methylate 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), and6also methylates α‐methylstyrene oxide (36) in α‐position to the phenyl residue with high selectivity, yielding nearly exclusively 2‐phenylpropanol (33) or 2‐methyl‐2‐phenylpropanol (37), respectively. The selective „α attack„ of Ag reagents is explained by fixation of the reagent to the phenyl residue of32and36in the first reaction step.