- Robust Alkyne Metathesis Catalyzed by Air Stable d2Re(V) Alkylidyne Complexes
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We report in this communication the first example of catalytic alkyne metathesis reactions mediated by well-defined non-d0 alkylidyne complexes. The air-stable d2 Re(V) alkylidyne complex Re4, bearing two PO-chelating ligands and a labile pyridine ligand, could catalyze homometathesis of internal alkynes with a broad substrate scope, including alcohols, amines, and even carboxylic acids. The catalyst can tolerate heating, air, and moisture in both solid and solution states, and the catalytic metathesis reactions could proceed normally in wet solvents.
- Cui, Mingxu,Bai, Wei,Sung, Herman H. Y.,Williams, Ian D.,Jia, Guochen
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supporting information
p. 13339 - 13344
(2020/09/03)
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- Rhodium-Catalyzed Cyclization of Terminal and Internal Allenols: An Atom Economic and Highly Stereoselective Access Towards Tetrahydropyrans
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A comprehensive study of a diastereoselective Rh-catalyzed cyclization of terminal and internal allenols is reported. The methodology allows the atom economic and highly syn-selective access to synthetically important 2,4-disubstituted and 2,4,6-trisubstituted tetrahydropyrans (THP). Furthermore, its utility and versatility are demonstrated by a great functional-group compatibility and the enantioselective total synthesis of (?)-centrolobine.
- Breit, Bernhard,Schmidt, Johannes P.
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supporting information
p. 23485 - 23490
(2020/10/29)
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- Rhodium catalyzed C-C bond cleavage/coupling of 2-(azetidin-3-ylidene)acetates and analogs
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The C-C bond cleavage/coupling of 2-(azetidin-3-ylidene)acetates with aryl boronic acids catalyzed by a rhodium complex was studied with a "conjugate addition/β-C cleavage/protonation" strategy.
- Yang, Xuan,Kong, Wei-Yu,Gao, Jia-Ni,Cheng, Li,Li, Nan-Nan,Li, Meng,Li, Hui-Ting,Fan, Jun,Gao, Jin-Ming,Ouyang, Qin,Xie, Jian-Bo
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supporting information
p. 12707 - 12710
(2019/10/28)
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- Rapid Metal-Free Formation of Free Phosphines from Phosphine Oxides
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A rapid method for the reduction of secondary phosphine oxides under mild conditions has been developed, allowing simple isolation of the corresponding free phosphines. The methodology involves the use of pinacol borane (HBpin) to effect the reduction while circumventing the formation of a phosphine borane adduct, as is usually the case with various other commonly used borane reducing agents such as borane tetrahydrofuran complex (BH3?THF) and borane dimethyl sulfide complex (BH3?SMe2). In addition, this methodology requires only a small excess of reducing agent and therefore compares favourably not just with other borane reductants that do not require a metal co-catalyst, but also with silane and aluminium based reagents. (Figure presented.).
- Provis-Evans, Cei B.,Emanuelsson, Emma A. C.,Webster, Ruth L.
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supporting information
p. 3999 - 4004
(2018/09/21)
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- Selective dehydrocoupling of phosphines by lithium chloride carbenoids
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The development of a simple, transition-metal-free approach for the formation of phosphorus-phosphorus bonds through dehydrocoupling of phosphines is presented. The reaction is mediated by electronically stabilized lithium chloride carbenoids and affords a variety of different diphosphines under mild reaction conditions. The developed protocol is simple and highly efficient and allows the isolation of novel functionalized diphosphines in high yields.
- Molitor, Sebastian,Becker, Julia,Gessner, Viktoria H.
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supporting information
p. 15517 - 15520
(2014/12/12)
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- A superior method for the reduction of secondary phosphine oxides
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(Chemical Equation Presented) Diisobutylaluminum hydride (DIBAL-H) and triisobutylaluminum have been found to be outstanding reductants for secondary phosphine oxides (SPOs). All classes of SPOs can be readily reduced, including diaryl, arylalkyl, and dialkyl members. Many SPOs can now be reduced at cryogenic temperatures, and conditions for preservation of reducible functional groups have been found. Even the most electron-rich and sterically hindered phosphine oxides can be reduced in a few hours at 50-70°C. This new reduction has distinct advantages over existing technologies.
- Busacca, Carl A.,Lorenz, Jon C.,Grinberg, Nelu,Haddad, Nizar,Hrapchak, Matt,Latli, Bachir,Lee, Heewon,Sabila, Paul,Saha, Anjan,Sarvestani, Max,Shen, Sherry,Varsolona, Richard,Wei, Xudong,Senanayake, Chris H.
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p. 4277 - 4280
(2007/10/03)
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- Ligand Electronic Effects in Asymmetric Catalysis: Enhanced Enantioselectivity in the Asymmetric Hydrocyanation of Vinylarenes
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The enantioselectivity of the nickel-catalyzed, asymmetric hydrocyanation of vinylarenes using glucosederived, chiral phosphinite ligands, L, increases dramatically when the ligands contain electron-withdrawing P-aryl substituents.The substrate and solvent also strongly influence the enantioselectivity, with the highest ee's (85-91percent for 6-methoxy-2-vinylnaphthalene (MVN)) obtained for the hydrocyanation of electron-rich vinylarenes in a nonpolar solvent such as hexane.Mechanistic studies suggest the catalytic cycle consists of an initial HCN oxidative addition or vinylarene coordination to "NiL", followed by insertion to form an (η3-benzyl)nickel cyanide complex, and irreversible reductive elimination of the nitrile.A kinetic analysis of the NiLa(COD) (La, P-aryl=3,5-(CF3)2C6H3) catalyzed hydrocyanation of MVN indicates that as the HCN concentration is increased the catalyst resting state shifts from NiLa(COD) to a complex containing both MVN and HCN, presumably the (η3-benzyl)nickel cyanide intermediate NiLa(η3-CH3CHC10H6OCH3)CN.A 31P NMR analysis of the intermediate NiLa(MVN) shows little ground state differentiation of the MVN enantiofaces and suggests that the enantioselectivity is determined later in the mechanism.Deuterium labeling studies suggest that electron-withdrawing P-aryl substituents increase the rate of reductive elimination of the product nitrile from the (η3-benzyl)nickel cyanide intermediate and, on this basis, a rationale for the ligand electronic effect is proposed.
- Casalnuovo, Albert L.,RajanBabu, T. V.,Ayers, Timothy A.,Warren, Timothy H.
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p. 9869 - 9882
(2007/10/02)
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