Search results for "cyclopropanation"
showing 10 items of 23 documents
A versatile rigid binucleating ligand for Rh2(μ-Cl)2 moieties: its application as a catalyst in hydrogenation and cyclopropanation
2003
A rigid non-deforming "MCl 2 M" binucleating ligand [7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 ] - able to held the two rhodium atoms in a cooperative distance has been synthesized. The original two bridging chlorides are retained in [Rh 2 (C 5 Me 5 ) 2 Cl 2 {7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 }] + . Hydrogenation of 1-hexene is 10 times faster with [Rh 2 (C 5 Me 5 ) 2 Cl 2 {7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 }] + than with [Rh 2 (C 5 Me 5 ) 2 Cl 4 ]. A hydrogenation mechanism has been proposed which assumes that [Rh 2 (C 5 Me 5 ) 2 (Cl)(H){7,8-μ-S(4'-C 6 H 3 (CH 3 ))S-C 2 B 9 H 1 0 }] + is the first generated species in the process.
Diastereoselective synthesis of antiquorin and related polyoxygenated atisene-type diterpenes
2007
Abstract A diastereoselective approach to polyoxygenated atisene-type diterpenes starting from (S)-(+)-carvone is described. The key steps used in the preparation of the atisene framework are an intramolecular Diels–Alder reaction, an intramolecular diazoketone cyclopropanation, an endocyclic cyclopropane ring cleavage and the regioselective reduction of an allylic bromide by a low-valent chromium species. The synthesis of natural atisanes antiquorin (1), atis-16-ene-3,14-dione (3), atis-16-ene-2,3,14-trione (8) and 3β-hydroxy-atis-16-ene-2,14-dione (9) following this approach is presented. Also described is the synthesis of 18-hydroxy-atis-16-ene-3,14-dione (5), the structure erroneously a…
Insight into the mechanism of diazocompounds transformation catalyzed by hetero cuboidal clusters [Mo3CuQ4(MeBPE)3X4]+, (Q=S, Se; X=Cl, Br): The cata…
2008
Abstract Two enantiomerically pure trinuclear compounds of formula (P)-[Mo3S4{(R,R)-Me–BPE}3Br3]Br and (P)-[Mo3Se4{(R,R)-Me–BPE}3Cl3]Cl, (P)-1b.Br and (P)-1c.Cl, respectively, have been synthesized in a good yield and a stereospecific manner by excision of polymeric [Mo3Q7X4]n (Q = S or Se, X = Cl or Br) phases with (R,R)-Me–BPE{1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane}. They have been transformed into chiral hetereo cuboidal compounds [Mo3S4{(R,R)-Me–BPE}3Br3]PF6, (P)-2b.PF6, and [Mo3Se4{(R,R)-Me–BPE}3Cl3]PF6, (P)-2c.PF6, by reaction with copper salts. All these compounds have been characterized by 31P NMR, IR, UV–Vis, mass spectrometry, elemental analysis, and chiral dichroism…
Enantio- and Diastereocontrol in Intermolecular Cyclopropanation Reaction of Styrene Catalyzed by Dirhodium(II) Complexes with Bulky ortho-Metalated …
2006
Enantiomerically pure dirhodium(II) complexes with ortho-metalated para-substituted aryl phosphines have been shown to lead to an enantio- and diastereoselective cyclopropanation of styrene with ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylate. High enantio- and diastereoselectivities are observed for the synthesis of ethyl cis-2-phenylcyclopropanecarboxylate using water as solvent. Additionally, a (+)-nonlinear effect, (+)-NLE, has been observed and studied in the asymmetric catalytic reaction developed in n-pentane.
Synthesis, reactions and structural features of monofluorinated cyclopropanecarboxylates
2002
Abstract Monofluorinated cyclopropanecarboxylates are available in racemic or optically active form by transition metal-catalyzed reactions of vinylfluorides with diazoacetates. From α-fluorostyrene and tert-butyl diazoacetate in the presence of 2 mol% of an enantiopure bis(oxazoline) copper complex, a 81:19 mixture of tert-butyl trans- and cis-2-fluoro-2-phenylcyclopropanecarboxylates was obtained with high enantiomeric excess (ee) of 93 or 89%, respectively. The corresponding racemic ethylesters were used as starting materials for the synthesis of carboxamides, of the cis- and trans-isomers of analogues of tranylcypromine, an anti-depressive drug and several of its homologous fluorinated …
Ruthenium titanocene and ruthenium titanium half-sandwich bimetallic complexes in catalytic cyclopropanation
2005
Abstract The reaction of the phosphine functionalised titanium half-sandwich complexes 7, 9 and 10 with the binuclear complex [(p-cymene)RuCl2]2 allowed the access to three new early-late bimetallic complexes (p-cymene)[(μ-η5:η1-C5H4(CH2)nPR2)TiX3]RuCl2 (11–13). The structure of 11 (n = 0, X = Cl) has been confirmed by X-ray diffraction. The ruthenium titanium half-sandwich bimetallic complexes so formed and the ruthenium titanocene analogues 4–6 catalyse the addition of ethyl diazoacetate to styrene with high selectivity toward cyclopropanation versus metathesis contrary to the monometallic complexes (p-cymene)RuCl2PR3.
Unprecedented Stereoselective Synthesis of Catalytically Active Chiral Mo3CuS4 Clusters
2005
Cluster excision of polymeric {Mo3S7Cl4}n phases with chiral phosphane (+)-1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane ((R,R)-Me-BPE) or with its enantiomer ((S,S)-Me-BPE) yields the stereoselective formation of the trinuclear cluster complexes [Mo3S4{(R,R)-Me-BPE}3Cl3]+ ([(P)-1]+) and [Mo3S4{(S,S)-Me-BPE}3Cl3]+ ([(M)-1]+), respectively. These complexes possess an incomplete cuboidal structure with the metal atoms defining an equilateral triangle and one capping and three bridging sulfur atoms. The P and M symbols refer to the rotation of the chlorine atoms around the C3 axis, with the capping sulphur atom pointing towards the viewer. Incorporation of copper into these trinuclear c…
Enantiocontrol in the intermolecular cyclopropanation reaction catalyzed by dirhodium(II) complexes with ortho-metalated aryl phosphine ligands
2001
(P) and (M) dirhodium(II) complexes with ortho-metalated aryl phosphines are assessed as chiral catalysts in the enantioselective cyclopropanation of styrenes by ethyl diazoacetate; enantioselectivities up to 91% and up to 87%, respectively, for cis- and trans-2-arylcyclopropanecarboxylates are observed. Barberis, Mario, Mario.Barberis@uv.es ; Lahuerta Peña, Pascual, Pascual.lahuerta@uv.es ; Perez Prieto, Julia, Julia.Perez@uv.es ; Sanau Torrecilla, Mercedes, Mercedes.Sanau@uv.es
Bimetallic complexes with ruthenium and tantalocene moieties: Synthesis and use in a catalytic cyclopropanation reaction
2006
Abstract The reaction of the tantalocene dichloride monophosphines ( 1 – 2 ) with the binuclear complex [( p -cymene)RuCl 2 ] 2 gives the heterobimetallic compounds ( p -cymene)[(η 5 -C 5 H 5 )(μ-η 5 :η 1 -C 5 H 4 (CH 2 ) 2 PR 2 )TaCl 2 ]RuCl 2 ( 3 – 4 ). The air oxidation of these bimetallic species 3 – 4 , leads to the cationic hydroxo tantalum ruthenium derivatives 5 – 6 . The last ones are easily deprotonated by a base to afford the oxo analogues 7 – 8 . A preliminary assessment in catalytic cyclopropanation of styrene with tantalum ruthenium bimetallic complexes 3 – 8 as precatalysts revealed a cooperative effect with a subtle role of the early metal fragment.
Enantio- and diastereocontrol in intermolecular cyclopropanation reaction of styrene catalyzed by dirhodium(II) complexes with bulky ortho-metalated …
2004
Enantiomerically pure dirhodium(II) complexes with ortho-metalated p-substituted aryl phosphines have been shown to be enantio- and diastereoselective in the cyclopropanation of styrene by ethyl diazoacetate. Enantioselectivities up to 91% and diastereoselectivities up to 90% are observed for ethyl cis-2-phenylcyclopropanecarboxylate. Estevan Estevan, Francisco, Francisco.Estevan@uv.es ; Lahuerta Peña, Pascual, Pascual.lahuerta@uv.es ; Lloret Fillol, Julio, Julio.Lloret@uv.es ; Sanau Torrecilla, Mercedes, Mercedes.Sanau@uv.es ; Ubeda Picot, M Angeles, Angeles.Ubeda@uv.es ; Vila Gomez, Jaume Llorenc, Jaume.Vila@uv.es