Tropolones and other products from a Reimer-Tiemann reaction

Abstract

The Reimer-Tiemann reaction on 4-methyl-, 4-ethyl-, and 4-propyl- guaiacols gave the corresponding normal 5-alkyl-2-hydroxy-3- methoxybenzaldehydes together with the minor products: 4-alkyl-4- dichloromethyl-2-methoxycyclohexa-2,5-dienones, 4-alkyl-5- chlorotropolones, 3-alkyl-4-chlorobenzoic acids, 6-alkyl-4-hydroxy-3- methoxybenzaldehydes, and 5-alkyltropolones. The minor aldehydes are formed from the dienones during workup by a dienone-phenol rearrangement, and the dienones yield the 5-alkyl-tropolones by the action of alkali. The acids are derived from the chlorotropolones by base-catalysed ring contraction. The chlorotropolones do not appear to be derived from the dienones but rather through direct addition of dichlorocarbene to the phenolate anions.