The synthesis of lactones. Part I: Saturated δ‐ and ϵ‐Lactones

A homologous series of δ- and ϵ-lactones has been synthesized, as well as some branched-chain δ-lactones. The δ-lactones have been prepared by oxidation of 2-alkylcyclopentanones or 2,5-dialkylcyclopentanones with Caro's acid or by hydrogenation of corresponding oxo acids. The latter were obtained by chromic acid oxidation of these 2-alkylcyclopentanones, or by Cason synthesis from 4-methoxycarbonyl-butanoyl chloride and dialkylcadmium, or by condensation of vinyl ketones with diethyl malonate. The alkylcyclopentanones were prepared by catalytic hydrogenation of 2-alkylidenecyclopentanones obtained by aldol condensation of cyclopentanone and alkanals. The 2,5-dialkylcyclopentanones, used as starting compounds for branched-chain δ-lactones, were obtained either by aldol condensation or by Dieckmann synthesis. A general method for the preparation of ϵ-lactones (lactonisation of 6-hydroxy acids under the influence of aromatic sulfonic acid) has been developed. Some physical constants of the pure compounds (including the intermediates) and of some of their characteristic derivatives have been determined.