The synthesis of lactones. Part II: Some 2‐alken‐5‐olides and 2,4‐dodecadien‐5‐olide

A series of 2‐alken‐5‐olides has been prepared from 1‐alkyn‐4‐ols by carbonation of their Grignard reagents and selective hydrogenation of the triple bond of the obtained 5‐hydroxy‐2‐alkynoic acids. The lactones were prepared by dehydration of the 5‐hydroxy‐2‐alkenoic acids. The reaction between 2‐alkenals and malonic acid to give 2,4‐dienoic acids also results in the formation of 2‐alken‐5‐olides as by‐products. 2,4‐Dodecadien‐5‐olide was prepared by bromination of 2‐dodecen‐5‐olide with N ‐bromosuccinimide followed by dehydrobromination.