CATALYTIC ACTION OF AZOLIUM SALTS .8. OXIDATIVE AROYLATION WITH ARENECARBALDEHYDES CATALYZED BY 1,3-DIMETHYLBENZIMIDAZOLIUM IODIDE

Refluxing of a mixture of benzaldehyde (la), 1,3-dimethylbenzimidazoli um iodide (7), p-nitroaniline (9b) as an oxidizing agent, and 1,8-diaz abicyclo[5,4,0]-7-undecene (DBU) in MeOH afforded methyl benzoate (2a) in good yield, Other methyl arenecarboxylates 2 were similarly obtain ed from arenecarbaldehydes 1, We showed that this aroylation proceeds via the 2-aroyl-1,3-dimcthylbenzimidazolium salt (8), The 1,2,4-triazo lium salt (18) and the naphtho[1,2-d]imidazolium salt (19) were also e ffective catalysts for this oxidative aroylation, However, the aroylat ion did not proceed with the imidazolium salt (20), Tn the presence of flavins (25a-c), arenecarbaldehydes 1 reacted in MeOH under aerobic c onditions catalyzed by the benzimidazolium salt 7 to give the correspo nding methyl arenecarboxylates 2, (10-phenylisoalloxazin-3-yl)propyl]b enzimidazolium bromide (27) is an effective complex catalyst for this oxidative aroylation.