New synthesis of vaulted biaryl ligands via the Snieckus phenol synthesis

reaction: see text] In an effort to develop a synthesis of the VAPOL ligand that avoids the use of a chromium carbene complex, a route was examined that involved the annulation of a naphthalene carboxamide via the method of Snieckus. The latter derivatives could be converted in a two-step sequence to 2-phenyl-4-phenanthrols in 60-72% overall yields. The utility of this method for the synthesis of VAPOL derivatives is demonstrated in the synthesis of (S)-7,7'-dimethyl-VAPOL.