title: Catalyst- and solvent-dependent stereodivergence in the intramolecular Et(2)Zn/Pd(0) -promoted carbonyl propargylation: mechanistic implications.
abstract: Carbonyl-tethered propargylic benzoates undergo intramolecular carbonylpropargylation upon treatment with Et2 Zn in the presence of a catalytic amount of Pd(0) with the formation of 2-alkynylcyclopentanol products. A ligand/solvent effect on the cis/trans selectivity (referring to the relative positions of alkynyl and OH groups) of ring-closure has been found. In a non-coordinating solvent (benzene), increasing the electron-donating ability of the phosphine ligand (while decreasing its dissociation ability) leads to an increased tendency towards the trans product. On the other hand, the combination of a coordinating solvent (THF) and PPh3 , an easily dissociated phosphine, results in the exclusive formation of cis products. Experimental and computational results are compatible with a divergent behavior of an allenylethylpalladium intermediate that partitions between competitive carbonyl-addition and transmetalation pathways, each leading to a different diastereoisomer. These results also suggest that the dissociating ability of the phosphine regulates that behavior.
authors: Departamento de Química Orgánica II, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao (Spain), Fax: (+34) 946-013500.
authors: Mónica
authors: M
authors: Arrate
authors: Aritz
authors: A
authors: Durana
authors: Paula
authors: P
authors: Lorenzo
authors: Ángel R
authors: ÁR
authors: de Lera
authors: Rosana
authors: R
authors: Álvarez
authors: José M
authors: JM
authors: Aurrecoechea
mesh_terms: D002384:Catalysis; D008024:Ligands; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D010293:Pargyline / Q000031:analogs & derivatives* / Q000737:chemistry*; D012997:Solvents; D013237:Stereoisomerism; D015032:Zinc / Q000737:chemistry*
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D012997:Solvents; D010165:Palladium; D010293:Pargyline; D015032:Zinc
keywords: allenylpalladium; cyclization; palladium; propargylic compounds; stereoselectivity; transmetalation