Magnesium hydrides and the dearomatisation of pyridine and quinoline derivatives


Hill, M., Kociok-Kohn, G., MacDougall, D. J., Mahon, M. F. and Weetman, C., 2011. Magnesium hydrides and the dearomatisation of pyridine and quinoline derivatives. Dalton Transactions, 40 (46), pp. 12500-12509.

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    Reactions of the -diketiminato n-butyl magnesium complex, [HC{(Me)CN(2,6-iPr2C6H3)} 2MgnBu], with a range of substituted pyridines and fused-ring quinolines in the presence of PhSiH3 has been found to result in dearomatisation of the N-heterocyclic compounds. This reaction is proposed to occur through the formation of an unobserved N-heterocycle- coordinated magnesium hydride and subsequent hydride transfer via the C2-position of the heterocycle prior to hydride transfer to the C4-position and formation of thermodynamically-favoured magnesium 1,4-dihydropyridides. This reaction is kinetically suppressed for 2,6-dimethylpyridine while the kinetic product, the 1,2-dihydropyridide derivative, was isolated through reaction with 4-methylpyridine (4-methylpyridine), in which case the formation of the 1,4-dihyropyridide is prevented by the presence of the 4-methyl substituent. X-ray structures of the products of these reactions with 4-methylpyridine, 3,5-dimethylpyridine and iso-quinoline comprise a pseudo-tetrahedral magnesium centre while the regiochemistry of the particular dearomatisation reaction is determined by the substitution pattern of the N-heterocycle under observation. The compounds are all air-sensitive and exposure of the magnesium derivatives of dearomatised pyridine and 4-dimethylaminopyridine (DMAP) to air resulted in ligand rearomatisation and the formation of dimeric 2- n2-n2-peroxomagnesium compounds which have also been subject to analysis by single crystal X-ray diffraction analysis. An unsuccessful extension of this chemistry to N-heterocycle hydrosilylation is suggested to be a consequence of the low basicity of the silane reagent in comparison to the pyridine substrates which effectively impedes any further interaction with the magnesium centres.


    Item Type Articles
    CreatorsHill, M., Kociok-Kohn, G., MacDougall, D. J., Mahon, M. F. and Weetman, C.
    Related URLs
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    DepartmentsFaculty of Science > Chemistry
    ID Code27912


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