Platinum-mediated intramolecular cyclization of biphenyl propargyl alcohol : highly regioselective synthesis of phenanthrenes

Abstract

Polycyclic aromatic hydrocarbons have received attention, especially in materials science, because of their utility in photoelectronic devices such as field-effect transistors, light emitting diodes, and solar cells. Most of the group consist of phenanthrene molecules are commonly biologically active. A variety of approaches for the development of their backbone have been established. The synthesis of phenanthrene skeleton has important values as they generally offer selective and efficient routes to functionalized derivatives directly from simple substrates in fewer steps and under mild reaction conditions. In our research on the synthesis of polycyclic aromatic hydrocarbons and their derivatives, we suggested new and facile synthetic methods for phenanthrene ring with regioselectivity. We envisioned that phenanthrene construction can be derived from ortho-propargyl biaryl derivative via transition metal-catalyzed intramolecular cyclization. The derivatives investigated showed a preference 6-endo cyclization over 5-exo mode, not observable in 7-endo-mode. The complex produces construction of the phenanthrene with a vinyl metal functional unit. The subsequent loss of hydroxyl group would afford α,β-unsaturated carbene functionality, thereby the competing the formation of the phenanthrene system. With the possibility of various transformation of the carbene, this intermediate underwent 1,2-H migration to afford vinylphenanthrene product. To demonstrate the pathway via a carbene intermediate in this reaction, the substrate which blocks of a 1,2-H migration was prepared. This substrate would respectively give the phenanthrene product, which reacted with acidic C–H bonds in good yield, resulting a platinum carbene intermediate is a key complex of the transformation for the synthesis of polycyclic aromatic hydrocarbons.