Transition metal catalyzed hydroarylation of olefins using unactivated substrates: Recent developments and challenges

The addition of aromatic C–H bonds across olefin CC bonds (olefin hydroarylation) is an important synthetic methodology for the preparation of alkylated arenes. Traditional methods utilizing Friedel–Crafts catalysts result in a significant waste stream and substantial polyalkyated products. In order to achieve high overall yield of monoalkylated compounds, Friedel-Crafts catalysis must be combined with a second transalkylation catalytic step. Reactions that incorporate substituted olefins are selective for branched products. In addition, the regioselective synthesis of disubstituted alkyl arenes is difficult to achieve. Recent development of transition metal based catalysts provides non-Friedel-Crafts pathways for the production of alkyl arenes. Systems based on Ru(II), Ir(III), and Pt(II) have been developed, and mechanistic studies have begun to provide insight into the details of these catalysts. Herein, we review recently published results in the area of transition metal catalyzed olefin hydroarylation with a comparison of known catalysts and discussion of challenges yet to be overcome.

Graphical abstractTraditional methods for the synthesis of alkyl arenes utilizing Friedel-Crafts catalysts result in significant waste and polyalkyated products. Recent development of catalysts based on Ru(II), Ir(III) and Pt(II) have provided non-Friedel-Crafts pathways for the production of alkyl arenes, and mechanistic studies of these systems have begun to provide insight into the details of catalysis and structure/activity relationships.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch highlights► We review new catalysts for olefin hydroarylation. ► We focus on transition metal catalysts that operate by a non-Friedel-Crafts mechanism. ► Unactivated substrates (e.g., benzene, ethylene, propylene) are discussed. ► Stability of catalysts must be improved. ► Regioselectivity for dialkylation and linear/branched selectivity must be improved.