| Abstract: | Halomethyl acetates ( 3 ) could be prepared from aliphatic, α,β‐unsaturated and aromatic aldehydes, as well as from alicyclic ketones with high yields in simple one‐pot reactions. Very often, the products didn't have to be purified and could directly be used for synthetic purposes after evaporation of the solvent. Obviously, the ‘bad reputation’ of the reaction in the literature stemed from the fact that the reactions didn't take place under the best conditions. Carbonyl compounds ( 1 ) and acyl halides ( 2 ) form equilibria which are completely on the side of the halomethyl acetates ( 3 ) at room temperature (starting with aliphatic and most aromatic aldehydes) and which can be strongly influenced by the reaction parameters. It is crucial to work at low temperature in apolar solvents and to remove (or deactivate) the catalyst before workup. Reactions may be realized with or without solvents. Side reactions were observed with formaldehyde and acetaldehyde but, with exception of formaldehyde, could be reduced close to zero (see Fig. 5). By‐products were essentially avoided if the reaction took place in apolar solvents and with a local excess of acetyl chloride. In many cases clean products were available which could directly be used for synthetic purposes. Halomethyl acetates ( 3 ) are bifunctional carbonyl derivatives with two different leaving groups, whose preparative advantages have been useful for the synthesis of various pentafulvenes, but were especially important for preparing unstable parent fulvenes and fulvalenes. |
