tert-Butoxycarbonyl as Convenient Nitrogen Protection During Alkylation of 2-Benzyl-4,5-dihydroimidazoles

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Abstract
Dèpartement de Pharmacochimie Molëculaire, Centre de Neurochimie du CNRS et Universitè Louis Pasteur, 5, rue B. Pascal, 67084-Strasbourg, Cedex, France. The tert-butoxycarbonyl group is a convenient protection for the N-1 nitrogen during alkylation of 2-benzyl-4,5-dihydro-imidazoles. As part of our search for ligands of γ-aminobutyric (GABA) receptors1 we investigated the preparation of β-aryl GABA 4a-c and 7a, according to the equivalence of basicity for the amino and the dihydroimidazole functions.2 Recently Jones et al.3 have reported the C-alkylation of 2-substituted-4,5-dihydroimidazoles via metalation, whilst a benzyl masking group was fixed at N-1 and finally removed with sodium in liquid ammonia. But owing to the strong conditions required for the removal of the N-benzyl group, we have been searching for an other protective group, compatible with the presence of an acetic function at a later stage and different from trimethyl- or tert-butyldimethylsilyl reported to be inoperative.3 Therefore we investigated the possibility to use the fert-butoxycarbonyl (Boc) protection for N-1 in the dihydroimidazole ring during C-alkylation.