Vilsmeier-Haack reactions (VHR) with acetanilides afforded 2-chloro 3-formyl quinoline derivatives. The reactions obeyed second order kinetics with a first order dependence on VHR as well as acetanilide. Significant rate enhancements were observed when transition metal ions such as Cu(II), Ni(II), Co(II), and Cd(II) were used as catalysts in these reactions. The kinetic results in transition metal ion catalyzed reactions coupled with uv-visible spectrophotometric observations substantiated the participation of mixed ligand precursors of the type [M(II)S(VHR)] involving acetanilides and VH reagents in the rate limiting step. Activation parameters were computed and interpreted suitably.
Aromatic compounds (phenols), when treated with Vilsmeier Haack (V-H) reagent in the presence of transition metal ions such as Cu(II), Ni(II), Co(II), Cd(II), and Zn(II) under reflux conditions, afforded corresponding ortho-formyl derivatives in good yields. Under normal conditions the metal-ion-free V-H reactions are too sluggish and resulted in poor yields. This protocol provides highly regioselective formylation under a mild and efficient condition with simple workup.
Vilsmeier–Haack (VH) formylation reactions with acetophenones are sluggish in acetonitrile medium even at elevated temperatures. However, millimolar concentrations of transition metal ions such as Cu(II), Ni(II), Co(II), and Cd(II) were found to exhibit efficient catalytic activity in Vilsmeier–Haack Reactions with acetophenones. Reactions are accelerated remarkably in the presence of transition metal ions. The VH reactions followed second order kinetics and afforded acetyl derivatives under kinetic conditions also irrespective of the nature of oxychloride (POCl3 or SOCl2) used for the preparation of VH reagent along with DMF. On the basis of UV–vis spectroscopic studies and kinetic observations, participation of a ternary precursor [M(II) S (VHR)] in the rate‐limiting step has been proposed to explain the mechanism of the metal ion–catalyzed VH reaction.
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