216976-33-9Relevant academic research and scientific papers
Efficient synthetic routes to terminal γ-keto-alkynes and unsaturated cyclic carbene complexes based on regio- and diastereoselective nucleophilic additions of enolates on ruthenium(II) indenyl allenylidenes
Cadierno, Victorio,Conejero, Salvador,Gamasa, M. Pilar,Gimeno, José,Pérez-Carre?o, Enrique,García-Granda, Santiago
, p. 3175 - 3189 (2001)
Ruthenium(II) indenyl allenylidene complexes [Ru{=C=C=C(R1)Ph}(η5-C9H7) (PPh3)2] [PF6] (R1 = Ph (1), H (2)) regioselectively react with lithium enolates LiCH2COR2 (R2 = Ph, iPr, Me, Fc, (E)-CH=CHPh) at the Cγ atom to yield the neutral σ-alkynyl derivatives [Ru{C≡CC(R1)Ph(CH2COR2)} (η5-C9H7)(PPh3)2] (3a-e, 4a-d). Protonation of 3a-e and 4a-d with HBF4·Et2O affords the cationic vinylidene derivatives [Ru{=C=C(H)C(R1)Ph(CH2COR2)}(η5- C9H7)(PPh3)2] [BF4] (5a-e, 6a-d), which can be easily demetalated, by treatment with acetonitrile, to yield the terminal γ-keto-substituted alkynes HC≡CC(R1)Ph(CH2COR2) (7a-e, 8a-d) and the nitrile complex [Ru(N≡CMe)(η5-C9H7) (PPh3)2][BF4] (9). The addition of lithium enolates LiCH2COR (R = Ph, iPr, Me) on the optically active allenylidene complex [Ru{=C=C=C(C9H16)}(η5-C9 H7)(PPh3)2][PF6] (12; C(C9H16) = (1R)-1,3,3-trimethylbicyclo[2.2.1]hept-2-ylidene) proceeds in a regio- and diastereoselective manner, affording σ-alkynyl derivatives [Ru{C≡CC(C9H16)(CH2COR)} (η5-C9H7)(PPh3)2] (13a-c). The X-ray crystal structure of 13b shows that these enolate additions take place on the less sterically congested exo face of the allenylidene chain. Chiral alkynes HC≡CC(C9H16)(CH2COR) (15a-c) have been also prepared from 13a-c via initial protonation with HBF4·Et2O and subsequent treatment of the resulting vinylidenes 14a-c with acetonitrile. Cyclic alkenyl derivatives [Ru{C=CHC(R1)(R2)CH=C(R3)O} (η5-C9H7)(PPh3)2] (R1 = R2 = Ph, R3 = Ph (18a), iPr (18b); R1R2 = C9H16, R3 = Ph (20)) have been obtained by treatment of dichloromethane solutions of σ-alkynyl complexes 3a,b and 13a with catalytic amounts of AlCl3 at room temperature. Protonation of these species affords the cyclic carbenes [Ru{=CCH2C(R1)(R2)CH=C(R3)O}- (η5-C9H7)(PPh3)2] [BF4] (19a,b, 21).
