The synthesis of alkylated or acylated nitroarene cyclopentadienyliron complexes: an alternative approach to the synthesis of arylated alkanoates

Abstract

Time-dependent oxidation of η⁶-alkylaniline-η⁵-cyclopentadienyliron hexafluorophosphates, 17–32, allows for the preparation of nitrobenzene complexes with alkyl 33–48 or keto 49 substituents. Alkylnitroarene complexes are prepared by the oxidation of their corresponding aniline complexes with H₂O₂ in CF₃CO₂H for 20 min. An increase in the reaction time to 24 h gives rise to nitroarene complexes with keto substituents in lower yields. The use of nitroarenes as starting materials in the synthesis of alkanoates is of importance since it allows for the preparation of a large number of this class of compounds with a variety of alkyl substituents. Two different approaches have been utilized to allow for the synthesis of alkanoates. The first approach involves nucleophilic aromatic substitution of alkylnitrobenzene complexes with ethyl alkylacetoacetates followed by demetallation to give the alkanoates. This methodology allows for the preparation of these esters with a variety of alkyl substituents in either the meta or para positions. Another route outlines the reaction of phenylsulfonylacetonitrile with nitroarene complexes to prepare alkanoic acid precursors with alkyl substituents in the ortho, meta and para positions. The preparation of a larger pool of nitroarene complexes clearly demonstrates the advantage of using the cyclopentadienyliron arene complexes in the synthesis of alkanoates or their precursors, arylated phenylsulfonylacetonitriles, over traditional synthetic routes.