Concerning the Structures of Alkali-Metal-Mediated ortho Zincation of Benzamides and Phenyl O-Carbamate

• Published in: Organometallics Vol. 30; no. 1; pp. 145 - 152
• Main Authors: Balloch, Liam, Kennedy, Alan R, Mulvey, Robert E, Rantanen, Toni, Robertson, Stuart D, Snieckus, Victor
• Format: Journal Article
• Language: English
• Published: American Chemical Society 10.01.2011
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om1009654

As a further contribution to alkali-metal-mediated metalation, a method for converting C−H bonds directly to C−Zn bonds without the need for an additional salt metathesis step, reactions of the sodium TMP-zincate [(TMEDA)Na(μ-TMP)(μ- t Bu)Zn( t Bu)] (1) with three different electron-rich aromatic substrates, have been investigated. Under ambient-temperature conditions, N,N-diethylbenzamide, N,N-diethyl-3-methoxybenzamide, and N,N-diethyl phenyl O-carbamate were zincated ortho to the substituent group (in between both substituents in the second case) in the crystalline products [(TMEDA)Na(μ-TMP){μ-2-[1-C(O)NEt2]C6H4}Zn( t Bu)] (3), [(TMEDA)Na(μ-TMP){μ-2-(1-C(O)NEt2)(3-OMe)C6H3}Zn( t Bu)] (4), and [(TMEDA)Na(μ-TMP){μ-2-(1-OC(O)NEt2)C6H4}Zn( t Bu)] (6). X-ray crystallography established that, in each case, the deprotonated aromatic fragment is captured by the residue of the bimetallic base, giving rise to seven-membered (NaNZnCCCO) ring structures for 3 and 4 and an eight-membered (NaNZnCCOCO) ring structure for 6. The new zincated aromatics were also characterized by solution-state 1H and 13C NMR spectroscopy. Reactivity studies of 3, 4, and 6 were also performed with iodine. In each case, three molar equivalents of iodine in THF solution gave the ortho-iodo products N,N-diethyl-2-iodobenzamide (7), N,N-diethyl-2-iodo-3-methoxybenzamide (8), and N,N-diethyl-2-iodophenyl-O-carbamate (9) in quantitative, 71% and 75% yields as determined by NMR analysis, respectively.