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You are using Science Of Synthesis as a Guest. Please login or sign up for a free trial to access the full content. Variation 3: Of Carbonyl Compounds

DOI: 10.1055/sos-SD-027-00291

Abbaspour Tehrani, K.; De Kimpe, N.Science of Synthesis, (200427341.

When ketones which have one α-methylene group are treated with N-(chloromethylene)-N,N-dimethylammonium chloride, 3-chloroprop-2-eniminium salts are obtained (e.g., iminium perchlorate 104 from acetophenone, Scheme 33).[‌160‌,‌161‌] The reaction is general for ketones but also works with aldehydes, which react more slowly. Ketones with two α-methylene groups can react with the Vilsmeier reagent several times.[‌162‌] Similar reactions can be performed with α,β-unsaturated aldehydes and ketones.[‌163‌] The reaction of 2 equivalents of N-(chloromethylene)-N,N-dimethylammonium chloride with carboxylic acids gives 3-(dialkylamino)prop-2-eniminium salts.[‌164‌,‌165‌] During the reaction carbon dioxide is formed. Simple aliphatic carboxylic acids do not react well with the Vilsmeier reagent unless they are substituted with a chloro, amino, aryl, or carboxyl group. Thus, substituted malonic acids 105 give 3-aminoalk-2-eniminium salts 106,[‌166‌,‌167‌] while malonic acid itself (105, R1=H) undergoes a triple reaction to give bis(iminium) perchlorate 107 (Scheme 33).[‌168‌] The reaction of bromoacetic acid with phosphoryl chloride/dimethylformamide gives the bis(iminium) salt of triformylmethane, 2-(dimethylamino)methylene-1,3-bis(dimethyliminio)propane dichloride.[‌169‌] Initially, this compound has been isolated as the bis(perbromide)[‌170‌] or bis(perchlorate), but for reasons of safety and better solubility in water it has been converted into the bis(fluoroborate) salt.

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