Ketene thioacetal route to .gamma.-lactones. Effect of carbonyl hardness on reaction-site selectivity and a unique preparation of 3-methyl-5-phenyl-2(5H)-furanone
[EN] NOVEL HETEROCYCLIC COMPOUNDS, PHARMACEUTICAL COMPOSITIONS CONTAINING THEM AND PROCESSES FOR THEIR PREPARATION [FR] NOUVEAUX COMPOSÉS HÉTÉROCYCLIQUES, COMPOSITIONS PHARMACEUTIQUES LES CONTENANT ET PROCÉDÉS POUR LEUR PRÉPARATION