THE CHEMISTRY OF STABLE CARBENES .2. BENZOIN-TYPE CONDENSATIONS OF FORMALDEHYDE CATALYZED BY STABLE CARBENES

Stable carbenes derived from thiazole, 1H-imidazole, and 4H-1,2,4-tria zole are efficient catalysts for benzoin-type condensations of formald ehyde. Catalysts derived from N-substituted thiazolium salts trimerize formaldehyde to dihydroxyacetone (II). Catalysts based on 1,4-disubst ituted 4H-1,2,4-triazol-1-ium salts give glycolaldehyde (I) as the mai n product and no II, whereas N,N'-disubstituted 1H-imidazol-3-ium salt s yield mixtures of both products. The isolation of several intermedia tes in the catalytic cycle provide a better insight into the reaction mechanism.