Double Protonation of Amino-Substituted Pyridine and Pyrimidine Tungsten Complexes: Friedel–Crafts-like Coupling to Aromatic Heterocycles

2-(Dimethylamino)­pyridine
(2-DMAP) and 2-(dimethylamino)­pyrimidine
derivatives form η2-bound complexes with the dearomatization
agent {TpW­(NO)­(PMe3)} that are each capable of undergoing
a double protonation. In the case of 2-DMAP, the resulting π-allyl
species reacts with the α-carbon of thiophene or 2-methylfuran,
thereby coupling the heterocyclic rings. In the case of the thiophene-derived
product, subsequent oxidative decomplexation using ceric ammonium
nitrate affords a novel organic amidine derivative. Examples of tungsten-promoted
acetylation and fluorination of the aminopyridine ring are also described.