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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

AuthorsCadierno, Victorio; Conejero, Salvador ; Gamasa, María Pilar; Gimeno, José; Pérez-Carreño, E. ; García-Granda, Santiago
KeywordsCarbene ruthenium
Unsaturated cyclic alkenyl
Organic synthesis
Issue Date12-Jun-2001
PublisherAmerican Chemical Society
CitationOrganometallics 20(14): 3175-3189 (2001)
AbstractRuthenium(II) indenyl allenylidene complexes [Ru{CCC(R1)Ph}(η5-C9H7)(PPh3)2][PF6] (R1 = Ph (1), H (2)) regioselectively react with lithium enolates LiCH2COR2 (R2 = Ph, iPr, Me, Fc, (E)-CHCHPh) at the Cγ atom to yield the neutral σ-alkynyl derivatives [Ru{CCC(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{CC(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 HCCC(R1)Ph(CH2COR2) (7a−e, 8a−d) and the nitrile complex [Ru(NCMe)(η5-C9H7)(PPh3)2][BF4] (9). The addition of lithium enolates LiCH2COR (R = Ph, iPr, Me) on the optically active allenylidene complex [Ru{CCC(C9H16)}(η5-C9H7)(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{CCC(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 HCCC(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 (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 (19a,b, 21).
Description15 páginas, 1 figura, 13 tablas, esquemas.
Publisher version (URL)http://dx.doi.org/10.1021/om010252o
Appears in Collections:(IIQ) Artículos
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