Stable carbenes derived from thiazole, 1H‐imidazole, and 4H‐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 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.

The article contains sections titled: 1. Introduction 1.1. Catalysts 1.1.1. Acidic Catalysts 1.1.2. Basic Catalysts 1.1.3. Organometallic Catalysts 1.2. Alkylating and Acylating Agents 1.3. Mechanism 1.3.1. Alkylation 1.3.2. Acylation 2. Alkylation and Acylation of Aromatic Compounds 2.1. Alkylation 2.1.1. Alkylation of Benzene 2.1.2. Cycloalkylation 2.1.3. Alkylation of Substituted Benzenes 2.1.4. Alkylation of Phenols 2.1.5. Alkylation of Aromatic Amines 2.1.6. Alkylation of Heteroaromatic Compounds and Related Substrates 2.1.7. Miscellaneous Alkylation Reactions 2.2. Acylation 2.2.1. Acylation of Benzene and Benzene Derivatives 2.2.2. Acylation of Polynuclear Aromatic Compounds 2.2.3. Acylation of Heteroaromatic Compounds 2.2.4. Acylation of Nonbenzenoid Aromatic Compounds 2.2.5. Miscellaneous Acylation Reactions 3. Acylation and Alkylation of Aliphatic Hydrocarbons 4. N ‐Alkylation and N ‐Acylation 4.1. N ‐Alkylation 4.1.1. N ‐Alkylation by Alcohols or Ethers 4.1.2. N ‐Alkylation by Alkyl Halides 4.1.3. N ‐Alkylation by Olefins 4.1.4. N ‐Alkylation by Carbonyl Compounds (Reductive Alkylation) 4.2. N ‐Acylation 5. O ‐Alkylation and O ‐Acylation 5.1. Synthesis of Esters 5.2. Synthesis of Anhydrides 5.3. Synthesis of Ethers 6. CH ‐Alkylation and CH ‐Acylation of Nonaromatic Compounds 7. Synthesis of Metal Alkyls

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Stable carbenes derived from thiazole, Iff-imidazole, and 4H-1,2,4-triazole are efficient catalysts for benzointype condensations of formaldehyde. Catalysts derived from N-substituted thiazolium salts trimerize formaldehyde to dihydroxyacetone (11). Catalysts based on 1,4-disubstituted 4H-1,2,4-triazol-l-ium salts give glycolaldehyde (I) as the main product and no 11, 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.

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