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

Liam Balloch, Alan R. Kennedy, Robert E. Mulvey, Toni Rantanen, Stuart D. Robertson, Victor Snieckus

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20 Citations (Scopus)

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.

Original languageEnglish
Pages (from-to)145-152
Number of pages8
JournalOrganometallics
Volume30
Issue number1
DOIs
Publication statusPublished - 10 Jan 2011

Keywords

  • directed ortho-metalation
  • tertiary aromatic amide
  • polysubstituted aromatics
  • deprotonative metalation
  • reaction pathway
  • reactivity
  • tmp-zincate

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