Synthesis of 2,4-dimethyl-6-oxo-2,4-heptadienoic acid derivatives from 2,4,6-trimethylpyrylium salts

Reaction 2,4,6-trimethylpyrylium salts with sodium cyanide in boiling water yielded the bicyclic lactone 1,3,5-trimethyl-6,8-dioxabicyclo[3.2.1]oct-2-en-7-one () along with a series of stereoisomers of 2,4-dimethyl-6-oxo-2,4-heptadienonitrile (), which were the sole products when the reaction was carried out at room temperature. Compound , along with 3,5-dimethylphenol (), was also obtained by refluxing briefly in aqueous sodium hydroxide. However, when was refluxed for a prolonged period in aqueous sodium acetate, 3,5-dimethyl-5-(2-oxopropyl)-furan-2-one (), along with some , was generated instead. Compound could also be produced from on prolonged refluxing with aqueous sodium acetate, indicating that was the kinetically-controlled and the thermodynamically-controlled product.