Reactivite des derives organomanganeux—VIII : Préparation de cétones par acylation d'organomanganeux. Influence de la nature de l'agent acylant,des solvants et des ligands

The influence of the nature of acylating reagents, solvents and ligands on the preparation of ketones by acylation of organomanganous reagents is studied. Thus acid chlorides in ether, symmetrical acid anhydrides in ether or THF and mixed carboxylic-carbonic anhydrides (R'COOCOOEt) in ether are compared, they lead to the corresponding ketones with good or excellent yields. Some problems of reproductibility are encountered and discussed when mixed anhydrides R'COOCOOEt are used in THF. The addition of a great variety of cosolvents (e.g. C₆H₆, AcOEt, CO₃Et₂, CH₂CN, CH₂CL₂, . .) to the reaction mixture before addition of the acylating reagent does not affect the yield of ketones. In comparison the complexation of organomanganous reagents by several ligands (e.g. Me₂S or Ph₃P) has no subsequent effect on their acylation. The main limitation for the choice of solvents or ligands is the use of amino derivatives which generally lead to a very low yield of ketones (e.g. C₅H₅N, TMEDA, Et₃N) or unreproducible yields (e.g. HMPA). Two applications of these studies are described:The stabilization of s or t-alkyl manganous derivatives by complexation which leads to the best yield of the corresponding ketonesThe use of a cosolvent in order to increase the yield when mixed anhydrides R'COOCOOEt are used in THF.