Conversion of meso-alkenes to chiral alkenes via titanocene-catalyzed ring-opening/ring-closing olefin metathesis

The preparation of 7-anti-(3-methyl-3-butenyl)norbornene 11 is described. This meso-symmetrical diene underwent ring opening/ring-closing olefin metathesis catalyzed by bis(cyclopentadienyl)titanacyclobutane 4 to give (1R*,6R*,7S*)-7-ethenyl-3-methylbicyclo[4.3.0]non-2-ene as a single diastereomer. The less-substituted 7-anti-(3-butenyl)norbornene 1 did not react selectively at the norbornene double bond. Related 7-ester-substituted norbornenes underwent stoichiometric ring-opening/ring-closing olefin metathesis to give single diastereomers of bicyclic ketones after acidic work-up. Attempts to form a chiral Tebbe-type complex from ansa-(2,2'-bis[8-(bicyclo[4.3.0]-nona-1(6),7-dienyl)]-1, 1'-binaphthyl)titanium dichloride 18 or a reactive chiral titanium carbene intermediate from its dimethyl derivative 20 were unsuccessful. (C) 1997 Elsevier Science S.A.