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Concerning the structures of alkali-metal-mediated ortho zincation of benzamides and phenyl o-carbamate

Balloch, Liam and Kennedy, Alan R. and Mulvey, Robert E. and Rantanen, Toni and Robertson, Stuart D. and Snieckus, Victor (2011) Concerning the structures of alkali-metal-mediated ortho zincation of benzamides and phenyl o-carbamate. Organometallics, 30 (1). pp. 145-152. ISSN 0276-7333

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Abstract

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(mu-TMP)(mu-Bu-t)Zn(Bu-t)] (1) with three different electron-rich aromatic substrates, have been investigated. Under ambient-temperature conditions, N,N-diethyl-benzamide, 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(mu-TMP){mu-2-[1-C(O)NEt2]C6H4}Zn(Bu-t)] (3), [(TMEDA)Na(mu-TMP){mu-2-(1-C(O)NEt2) (3-OMe)C6H3}Zn(Bu-t)] (4), and [(TMEDA)Na(mu-TMP){mu-2-(1-C(O)NEt2)C6H4}-Zn(Bu-t)] (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 H-1 and C-13 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.