CONVERSION OF MESO-ALKENES TO CHIRAL ALKENES VIA TITANOCENE-CATALYZEDRING-OPENING RING-CLOSING OLEFIN METATHESIS/

The preparation of 7-anti-(3-methyl-3-butenyl)norbornene 11 is describ ed. This meso-symmetrical diene underwent ring opening/ring-closing ol efin metathesis catalyzed by bis(cyclopentadienyl)titanacyclobutane 4 to give 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-clo sing olefin metathesis to give single diastereomers of bicyclic ketone s after acidic work-up. Attempts to form a chiral Tebbe-type complex f rom 2,2'-bis[8-(bicyclo[4.3.0]-nona-1(6),7-dienyl)]-1, 1'-binaphthyl)t itanium dichloride 18 or a reactive chiral titanium carbene intermedia te from its dimethyl derivative 20 were unsuccessful. (C) 1997 Elsevie r Science S.A.