CHIRAL AZOLE DERIVATIVES .2. SYNTHESIS OF ENANTIOMERICALLY PURE 1-ALKYLIMIDAZOLES

4,5-Dicyanoimidazole has been reacted with racemic and enantiopure alcohols 7 (entries 1-7 in Table 1) under Mitsunobu conditions to give 1-alkyl-4,5-dicyanoimidazole derivatives 8, which in turn have been transformed by hydrolysis and decarboxylation into 1-alkylimidazoles 10 in good overall yield and high enantiomeric excess. In contrast, when applied to benzyl and benthydryl alcohols (entries 8-15), this sequence afforded the final compounds in good overall yield, but as racemic mixtures. The 1-(1-phenylalkyl)imidazole derivative (S)-(+)-24 was, however, prepared in enantiopure form starting from the corresponding (S)-(-)-alpha-methylbenzylamine (21) using the Marckwald procedure, which entailed the alkylation of 21 with bromoacetaldehyde dimethyl acetal, followed by the construction of the imidazole ring through reaction with potassium thiocyanate and final Ra-Ni desulfuration. Following the same procedure, (S)-(+)-10c was also synthesized, proving the stereochemical outcome of the Mitsunobu reaction.