- Base-Promoted/Gold-Catalyzed Intramolecular Highly Selective and Controllable Detosylative Cyclization
-
A highly selective, controllable and synthetically useful base-promoted intramolecular detosylative cyclization of bis-N-tosylhydrazones has been achieved, affording N-containing heterocycles and cyclic olefins under transition-metal-free or gold-catalyzed procedures, respectively. Moreover, an effective and practical metal-free or gold-catalyzed approach to synthesize polycyclic aromatic compounds is also reported. Basic cyclizations: A highly selective, controllable, and synthetically useful base-promoted intramolecular detosylative cyclization of bis-N-tosylhydrazones affords N-containing heterocycles and cyclic olefins under transition-metal-free or gold-catalyzed procedures, respectively. Moreover, an effective and practical metal-free or gold-catalyzed approach to synthesize polycyclic aromatic compounds is also reported.
- Zhu, Chenghao,Qiu, Lin,Xu, Guangyang,Li, Jian,Sun, Jiangtao
-
supporting information
p. 12871 - 12875
(2015/09/07)
-
- Rhodium(II)-catalyzed cyclization of bis(N-tosylhydrazone)s: An efficient approach towards polycyclic aromatic compounds
-
Ahead of the PAC: Polycyclic aromatic compounds (PACs) can be easily accessed by the combination of Suzuki-Miyaura cross-coupling and a [Rh 2(OAc)4]-catalyzed carbene reaction using easily available bis(N-tosylhydrazone)s as intermediates (see scheme; Ts=4-toluenesulfonyl). Copyright
- Xia, Ying,Liu, Zhenxing,Xiao, Qing,Qu, Peiyuan,Ge, Rui,Zhang, Yan,Wang, Jianbo
-
supporting information; experimental part
p. 5714 - 5717
(2012/07/28)
-
- Reductive coupling of carbonyl compounds promoted by cobalt or titanium nanoparticles
-
The reaction of a series of aldehydes and ketones with readily prepared cobalt or titanium nanoparticles, under mild reaction conditions, led to the obtention of different reductive dimerization products depending on the nature of the transition metal used. Cobalt nanoparticles (CoNPs) allowed the selective transformation of the starting carbonyl compounds into vicinal diols, whereas the reaction promoted by titanium nanoparticles (TiNPs) led to the formation of the corresponding alkenes. In this last case, the use of trimethylsilyl chloride (TMSCl) as additive, at 0 °C, also allowed the obtention of vicinal diols after acidic aqueous work-up. ARKAT-USA, Inc.
- Nador, Fabiana,Mascaro, Evangelina,Castro, Melisa,Vitale, Cristian,Radivoy, Gabriel
-
p. 312 - 326
(2011/06/17)
-
- A versatile palladium catalyst system for Suzuki-Miyaura coupling of alkenyl tosylates and mesylates
-
A general and effective palladium system for Suzuki-Miyaura coupling of alkenyl electrophiles under mild reaction conditions is reported. With the Pd(OAc)2/CM-phos system, a variety of alkenyl tosylates are coupled well with ArB(OH)2. Moreover, the first successful examples of using alkenyl mesylates in alkenylation are also described.
- Wong, Pui Yu,Chow, Wing Kin,Chung, Kin Ho,So, Chau Ming,Lau, Chak Po,Kwong, Fuk Yee
-
supporting information; experimental part
p. 8328 - 8330
(2011/09/14)
-
- Well-defined air-stable palladium HASPO complexes for efficient Kumada-Corriu cross-couplings of (Hetero)aryl or alkenyl tosylates
-
Palladium complexes of representative heteroatom-substituted secondary phosphine oxide (HASPO) preligands were synthesized and fully characterized, including X-ray crystal structure analysis. Importantly, these well-defined complexes served as highly efficient catalysts for Kumada-Corriu cross-coupling reactions of aryl, alkenyl, and even heteroaryl tosylates. Particularly, an air-stable catalyst derived from inexpensive PinP(O)H displayed a remarkably high catalytic efficacy, which resulted in cross-couplings at low catalyst loadings under exceedingly mild reaction conditions with ample scope.
- Ackermann, Lutz,Kapdi, Anant R.,Fenner, Sabine,Kornhaab, Christoph,Schulzke, Carola
-
supporting information; experimental part
p. 2965 - 2971
(2011/05/05)
-
- Selective heck arylation of cyclohexene with homogeneous and heterogeneous palladium catalysts
-
Palladium catalysts containing Pd(II) supported on Al2O 3 and alumina-based mixed oxides, Al2O3- ZrO2, Al2O3-CeO2, and Al 2O3-Fe2O3, are very effective in the Heck coupling of iodobenzene with cyclohexene in DMF solution. The best results, up to 81% of monoarylated products with a selectivity to 4-phenylcyclohexene (3) close to 90% were obtained with KOH as a base. The catalytic activity of palladium supported on aluminabased oxides was compared with that of homogeneous precursors, such as Pd(OAc)2 and PdCl 2(PhCN)2, used in [Bu4N]Br as the reaction medium. Under such conditions homogeneous systems were more selective and produced up to 60% of monoarylated products with a selectivity to 3 close to 60%. Copyright
- Mieczynska, Ewa,Trzeciak, Anna M.
-
scheme or table
p. 2166 - 2177
(2010/08/04)
-
- Carbonyl coupling reactions catalytic in titanium and the use of commercial titanium powder for organic synthesis
-
The high thermodynamic stability of titanium oxides formed as the inorganic byproducts in McMurry-type reactions has so far prevented the development of a catalytic procedure for such reductive carbonyl coupling processes. Similarly, a tightly bound oxide layer passivates the surface of commercial titanium, which is unreactive toward organic substrates under conventional conditions. This paper outlines a way to overcome both of these problems. Thus, oxoamides 1a-h can be reductively cyclized to indoles 2a-h using only catalytic amounts of low-valent titanium if the reaction is carried out in the presence of a chlorosilane. Specifically, the method is based upon the in situ generation of an activated titanium species from TiCl3 and Zn in the presence of the substrate, followed by regeneration of titanium chloride from the titanium oxides formed via ligand exchange with the admixed chlorosilane. Its proper choice is crucial for obtaining both good turnover numbers and clean conversions. Depending on the product structure, (TMS)Cl, ClMe2SiCH2CH2SiMe2Cl (5), or ClMe2Si(CH2)3CN (6) was found to be best suited. Similarly, chlorosilanes also effect the activation of commercial titanium powder which may then be used as a performant off-the-shelf reagent for various types of carbonyl and acetal coupling reactions, for the deoxygenation of epoxides and for the reductive cyclization of oxoamides or oxoesters to indoles, benzofurans, and 2-quinolones. Under these conditions retinal can be reductively dimerized to β-carotene in good yield. Moreover, the titanium/ chlorosilane reagent combination exhibits a strong template effect, allowing macrocyclization reactions without recourse to high dilution. Up to 36-membered rings have been closed in that way. 29Si NMR studies provide some insight into the elementary steps responsible for the degradation of the surface oxide layer on titanium by the chlorosilane. The effect of Lewis acid additives on the course of the coupling processes is discussed.
- Fürstner, Alois,Hupperts, Achim
-
p. 4468 - 4475
(2007/10/02)
-
- "Site Selective" Formation of Low-Valent Titanium Reagents: An "Instant" Procedure for the Reductive Coupling of Oxo Amides to Indoles
-
Aromatic acylamido carbonyl compounds are readily cyclized to indole derivatives upon treatment with low-valent titanium reagents of the formal oxidation states 0, +1, and +2.Other strong reducing agents such as SmI2 and low-valent zirconium, niobium, and tungsten complexes are also capable of effecting such intramolecular alkylidenation reactions of amides.From the preparative point of view these heterocycle syntheses are best effected with an active titanium species which is prepared in the presence of the carbonyl compound upon coordination of TiCln (n = 3, 4) to the oxo amide substrate and reduction of this complex with zinc dust ("instant" method).This procedure turned out to be as effective as the titanium-graphite-based methodology previously described but is much easier to perform as all hazardous reagents are avoided. "Instant" cyclizations can also be run in nonetheral solvents such as DMF, ethyl acetate, or acetonitrile and turned out to be compatible with many functional groups.The method was used to cyclize oxo amide 15 to (+)-aristoteline, and it applies nicely to the synthesis of strained indole derivatives, the formation of benzofurans, conventional McMurry reactions of aldehydes and ketones, and the dimerization of alkynes.Metals such as zirconium can also be activated in situ by reduction of ZrCl4 in the presence of a carbonyl compound.On the basis of the results obtained with substrates bearing appropriate structural probes a mechanism for such intramolecular keto-amide coupling processes is proposed.Carbonyl dianions, formed upon two-electron reduction of the keto group, are the most likely reactive intermediates.Electrochemical investigations support this mechanistic interpretation.
- Fuerstner, Alois,Hupperts, Achim,Ptock, Arne,Janssen, Edo
-
p. 5215 - 5229
(2007/10/02)
-
- Formation and Reactivity of ?-Radical Cation Intermediates in the C-C Coupling Reaction of Phenyldiazomethanes by One-Electron Oxidation
-
One-electron oxidation of phenyldiazomethanes afforded cis-stilbene predominantly.The reaction was independent of the oxidation methods, e.g., electrolysis, copper(II), triarylaminium salts, or photosensitized one-electron oxidtions.The C-C coupling reaction was retarded by introducing α-substituents on phenyldiazomethanes.The ESR spectra of diazoalkane radical cations could be obtained during the electrolysis at low temperature and the resulting spectra revealed their unique electronic structure as ?-radicals for most cases.When a bulky tert-butyl group was substituted, the corresponding ?-radical cation was observed, but the C-C coupling reaction did not occur.The novel HOMO-LUMO switching by one-electron removal from the HOMO ?-orbital of diazomethane is explained by the interaction of phenyl group with the C-N-N ?-radical moiety.The C-C coupling reaction proceeds via facile cycloaddition between the diazomethane and ?-radical cation, and the preferential formation of cis-olefins is based on the secondary orbital interaction between the two phenyl groups.The structure and the stability of radical cation intermediates are rationalized on the basis of ab initio calculations.
- Ishiguro, Katsuya,Ikeda, Masatoshi,Sawaki, Yasuhiko
-
p. 3057 - 3066
(2007/10/02)
-
- Diazomethane Radical Cations as a Dipolarophile in the Dimeric Olefin Formation from Diazo-compounds
-
A novel cycloaddition mechanism involving diazomethane radical cations is proposed for the dimeric olefin formation by the one-electron oxidation of the diazo-compounds.The preference of cis-stilbene formation from phenyldiazomethane is understood by a secondary orbital interaction of phenyl groups on the cycloaddition step.
- Ishiguro, Katsuya,Sawaki, Yasuhiko,Iwamura, Hiizu
-
p. 1853 - 1856
(2007/10/02)
-