Novel Concepts in Directed Biaryl Synthesis, IX. Synthesis and Structure of Benzonaphthopyranones, Useful Bridged Model Precursors for Stereoselective Biaryl Syntheses

Abstract

Abstract A practicable two‐step procedure for the preparation of a series of lactone‐type bridged biaryls 7 as favorable substrates for subsequent atropisomer‐selective ring‐opening reactions is described. Due to the efficiency of the coupling step, which tolerates even a tert ‐butyl group next to the biaryl axis and avoids problems of regioselectivity, a variety of differently substituted representatives is prepared. These cover a broad range of steric hindrance and thus molecular distortion. The structures are investigated mainly by NMR spectroscopy and X‐ray diffraction, showing the lactones 7 to be helically distorted, depending on the size of the residues R.