Reactivity of Electron Deficient Arenes Upon Coordination to the Tungsten Dearomatization Agent {WTp(NO)(PMe3)}

Current limitations of traditional organic synthetic methodologies hinder the facile synthesis of elaborate three-dimensional organic molecules. In an effort to address this synthetic deficiency, a range of dearomatization methodologies have been developed over the years that provide access to alicyclic structures with multiple stereocenters from readily available aromatic molecules. The research described here focuses on electron rich transition metal dearomatization.
The exceptionally π-basic metal fragments {WTp(NO)(PMe3)} and {MoTp(NO)(DMAP)} (Tp = tris(pyrazolyl)- borate; DMAP = 4-(N,N-dimethylamino)pyridine) are able to bind across a single alkene bond of an aromatic molecule in a dihapto fashion, effectively dearomatizing the aromatic upon coordination. The ability of the tungsten fragment to form thermally stable η2-coordinated complexes with a variety of electron-deficient arenes is explored.
Sulfone functionalized trisubstituted cyclohexenes were prepared from two sequential tandem protonation/nucleophilic additions to a phenyl sulfone (PhSO2R; R = Me, Ph, NC4H8) dihapto-coordinated to the tungsten fragment. Such coordination renders the aryl ring susceptible to protonation at a carbon ortho to the sulfone group. The resulting arenium species readily reacts with the first nucleophile to form a dihapto-coordinated diene complex. The protonation/nucleophilic addition process can be repeated for the diene complex, rendering a sulfone functionalized trisubstituted cyclohexene.
A novel process is described for the synthesis of cyclohexenes bearing up to three substituents through the elimination of the sulfone moiety. These compounds are prepared from three independent nucleophilic addition reactions to the η2-phenyl sulfone systems. In certain cases, the protonation/nucleophilic addition process for the diene complex renders an allyl sulfone species. The allyl sulfone in turn can undergo a process in which a third nucleophile replaces the sulfone.
The last section focusses on amine additions to the η2-phenyl sulfone systems at various stages of the overall reaction scheme. The successful addition of secondary and aromatic amines as first nucleophiles is shown. An intramolecular lactamization occurs with the use of a primary amine as the second nucleophile, when the system is already functionalized by an ester. Upon formation of the lactam, the sulfone eliminates and a range of third nucleophilic additions are shown for the bicyclic system.