7. The chemistry of stable carbenes: Part 2 - Benzoin-type condensations of formaldehyde catalyzed by stable carbenes

Article abstract of DOI:10.1002/hlca.19960790108

Stable carbenes derived from thiazole, 1 H-imidazole, and 4H -1,2,4-triazole are efficient catalysts for benzoin-type condensations of formaldehyde. Catalysts derived from N-substituted thiazolium salts trimerize formaldehyde to dihydroxyacetone (II). Catalysts based on 1,4-disubstituted 4H-1,2,4-triazol-1-ium salts give glycolaldehyde (I) as the main product and no II, whereas N,N′-disubstituted 1H-imidazol-3-ium salts yield mixtures of both products. The isolation of several intermediates in the catalytic cycle provide a better insight into the reaction mechanism.