Alkyliron and Alkylcobalt Reagents, VIII. – Alkyl-Iron(II) Compounds as Reagents and Catalysts for the Transformation of Acyl Chlorides into Ketones
Me2Fe, Bu2Fe, Me3FeLi, or Bu3FeLi – prepared in situ by reduction of FeCl3 to FeCl2 and subsequent alkylation with MeLi, MeMgBr, BuLi, or BuMgBr – are useful reagents for the conversion of acyl chlorides into ketones. The system (RMgX + catalytic amount of FeCl3) react like the alkyl FeII reagents with acyl chlorides to give ketones even at –65°C. Competition experiments with benzoyl chloride/2-methoxy-benzoyl chloride show that the selectivity increases (competition constants Kk9.9, 10.7, 10.9, 15.0, ca. 110) in the sequence MeFeCl, Me2Fe, Me3Fe(MgBr), Me4Fe(MgBr)2, and catalytic system [MeMgBr + 2.5 mol % FeCl3] (= 2, 3, 4, 5, and 40 MeMgBr per 1 FeCl3, respectively). A new hypothesis on the nature of the active catalyst is discussed.