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

Abstract

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