The Chemistry of Stable Carbenes. Part 2. Benzoin‐type condensations of formaldehyde catalyzed by stable carbenes

Abstract Stable carbenes derived from thiazole, 1 H ‐imidazole, and 4 H ‐1,2,4‐triazole are efficient catalysts for benzointype condensations of formaldehyde. Catalysts derived from N ‐substituted thiazolium salts trimerize formaldehyde to dihydroxyacetone ( II ). Catalysts based on 1,4‐disubstituted 4 H ‐1,2,4‐triazol‐1‐ium salts give glycolaldehyde ( I ) as the main product and no II , whereas N,N ′‐disubstituted 1 H ‐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.