2,5-Dilithiation of N-protected imidazoles. Syntheses of 2,5-disubstituted derivatives of 1-methoxymethyl-, 1-triphenylmethyl-, and 1-(N,N-dimethylsulphonamido)-imidazole
Abstract
The conditions previously established for the dilithiation of 1-methylimidazole are shown to be applicable to 1-methoxymethyl- and 1-triphenylmethyl-imidazole allowing good-yielding syntheses of 1,2,5-trisubstituted imidazole derivatives. The suitability of the 1 -substituents (and of other groups) for the N-protection of imidazoles in dilithiation experiments is discussed and the use of the N,N-dimethyl-sulphamoyl protecting group is proposed. 1-Sulphamoylimidazole undergoes mono- and 2,5-di-lithiation quantitatively at low temperatures and in short reaction times. The results of work-up of the 2,5-dilithio intermediate with 1 mol equiv. of iodomethane or dimethyl sulphate indicate selectivity in favour of reaction at the 5-position.
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