Synthesis of Verbenindenes: A New Class of Chiral Indenyl Ligands Derived from Verbenone

A new class of chiral indenes (verbenindenes), in which a verbenone moiety is annulated to an indene core, is prepared by a sequence of Shapiro lithiation and Nazarov cyclization reactions. Since the initial indenes are resistant to deprotonation, they are isomerized via [1,5]-sigmatropic shifts to obtain indenes that are readily deprotonated with n-butyllithium. Reaction of the indenide anions with chloro(1,5-cycloctadiene)rhodium dimer produces verbenindenyl transition-metal complexes. Coordination of the indenyl ligand may occur with the gem-dimethyl bridge of the verbenone moiety syn or anti to the metal. Selectivity favors the less hindered anti complexes, and a crystal structure of a member of this series is presented.