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Regiochemistry of N‐substitution of some 4(5)‐substituted imidazoles under solvent‐free conditions
Author(s) -
Oresmaa Larisa,
Taberman Helena,
Haukka Matti,
Vainiotalo Pirjo,
Aulaskari Paula
Publication year - 2007
Publication title -
journal of heterocyclic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.321
H-Index - 59
eISSN - 1943-5193
pISSN - 0022-152X
DOI - 10.1002/jhet.5570440632
Subject(s) - chemistry , imidazole , nitrile , zinc , triethylamine , catalysis , potassium carbonate , benzyl chloride , aldehyde , organic chemistry , chloride , solvent , regioselectivity , medicinal chemistry , inorganic chemistry , polymer chemistry
Imidazole‐4(5)‐carboxaldehyde and 4(5)‐cyanoimidazole were N‐benzylated and N‐methylated using benzyl chloride and methyl iodide on zinc oxide (ZnO), alumina, and KF/alumina under basic conditions without solvent. Triethylamine (Et 3 N) or potassium carbonate was added as base in the reactions on ZnO and alumina. Imidazole‐4(5)‐carboxaldehyde was also benzylated on silica and carbon nanotubes. The effect of bases and solids on the product distribution of 1,4‐ and 1,5‐substituted compounds was investigated. In some cases, the product ratios were different for imidazole‐4(5)‐carboxaldehyde and 4(5)‐cyanoimidazole. In the reactions on KF/alumina the 1,4‐product was favored for both compounds. The combination of Et 3 N and ZnO favored the 1,5‐product, however for the nitrile effect was not so pronounced. When N‐benzylation and methylation of the aldehyde were performed in the presence of catalytic amount of zinc chloride with Et 3 N as base, the product distributions were the same as in the reactions on ZnO. Nitrile gave different product ratios on ZnO and in the presence of ZnCl 2 . In addition, a mixture of N‐benzylimidazole and 1,3‐dibenzylimidazolium was produced when imidazole was benzylated on KF/alumina. Only the latter product was afforded when two equivalents of benzyl chloride were used.