Heterohelicenes with embedded P-chiral 1H-phosphindole or dibenzophosphole units: diastereoselective photochemical synthesis and structural characterization

Abstract

The oxidative photocyclization reactions of olefins that contain 1H-phosphindole or dibenzophosphole substituents have been applied to the synthesis of P/N-bi-heterosubstituted dimeric helicenes, as well as of new [6]- and [8]phosphahelicenes. In these photocyclization processes, the configuration of the stereogenic phosphorus center dictates the sense of helical chirality. Thus, by starting from enantiomerically pure P-menthylphosphole-oxide units, this method affords enantiopure helical compounds. The helical phosphine oxides were characterized by X-ray diffraction. After reduction of the phosphine-oxides, the corresponding helical phosphines have been used as ligands in transition-metal complexes. The X-ray crystal structure of a gold chloride complex of a [6]helicene is reported.

Keywords: dibenzophospholes; enantioenriched helicenes; gold complexes; phosphahelicenes; photocyclization.