- Highly Selective Hydrogenation of Aromatic Ketones and Phenols Enabled by Cyclic (Amino)(alkyl)carbene Rhodium Complexes
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Air-stable Rh complexes ligated by strongly σ-donating cyclic (amino)(alkyl)carbenes (CAACs) show unique catalytic activity for the selective hydrogenation of aromatic ketones and phenols by reducing the aryl groups. The use of CAAC ligands is essential for achieving high selectivity and conversion. This method is characterized by its good compatibility with unsaturated ketones, esters, carboxylic acids, amides, and amino acids and is scalable without detriment to its efficiency.
- Wei, Yu,Rao, Bin,Cong, Xuefeng,Zeng, Xiaoming
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supporting information
p. 9250 - 9253
(2015/08/11)
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- Regio- and stereoselective cyclization reactions of unsaturated silyl enol ethers by photoinduced electron transfer - Mechanistic aspects and synthetic approach
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Oxidative photoinduced electron transfer (PET) reactions have been performed with various silyl enol ethers and silyloxy-2H-chromones bearing an olefmic or silylacetylenic side chain. The reactions result in regioselective ring closure with the formation of bi- to tetracyclic ring systems with a well-defined ring juncture, e.g. perhydrophenanthrenones 13 or benzo-annellated xanthenones 24. Our investigations have focussed on the optimization of this cychzation method with regard to irradiation time and product yield. The irradiation times could be reduced by using the cosensitized PET method. Modifying the substrate at the silyl group led to enhanced yields. In addition, we found that solvent and pressure dependences are important tools, allowing control of the regiochemistry. Both the synthesis of 6-endo products by radical cationic reaction pathways, as well as 5-exo ring closure by radical intermediates was achieved. Mechanistic details, including findings from deuterium labelling experiments, are discussed.
- Hintz, Sandra,Mattay, Jochen,Van Eldik, Rudi,Fu, Wen-Fu
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p. 1583 - 1596
(2007/10/03)
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- Acyl Radicals: Intermolecular and Intramolecular Alkene Addition Reactions
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A full study of the use of phenyl selenoesters as precursors to acyl radicals and their subsequent participation in intermolecular and intramolecular alkene addition reactions is detailed.Primary alkyl-, vinyl-, and arylsubstituted acyl radicals generated by Bu3SnH treatment of the corresponding phenyl selenoesters participate cleanly in intermolecular addition reactions with alkenes bearing electron-withdrawing or radical-stabilizing substituents at rates that exceed those of the potentially competitive decarbonylation or reduction.Similarly, their intramolecular addition to activated or unactivated alkenes proceeds without significant competitive reduction or decarbonylation and at rates generally >/= 1 x 106 s-1 with some occuring at rates >/= 3 x 107 s-1.Consistent with their behavior in intermolecular addition reactions, the 5-exo-trig cyclizations of secondary and tertiary alkyl-substituted acyl radicals to an unactivated olefin acceptor may be accompanied by varying degrees of decarbonylation, even under low-temperature free-radical conditions.Studies are presented which suggest that the intramolecular additions of acyl radicals to alkenes under the conditions detailed herein may be regarded as irreversible, kinetically controlled processes which exhibit regioselectivity that is predictable based on well-established empirical rules set forth for the analogous free-radical cyclization reactions of alkyl radicals.
- Boger, Dale L.,Mathvink, Robert J.
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p. 1429 - 1443
(2007/10/02)
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- Acyl Radicals: Functionalized Free Radicals for Intramolecular Cyclization Reactions
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A study describing the use of phenyl selenoesters as direct precursors to acyl radicals suitable for the initiation of intramolecular free-radical cyclization reactions is detailed.
- Boger, Dale L.,Mathvink, Robert J.
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p. 3377 - 3379
(2007/10/02)
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- Trimethylsilyl Cyanide - A Reagent for Umpolung, XII. Intramolecular Diels-Alder Reaction of Dienals via Umpolung
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Umpolung of dienals 1 and 2 with trimethylsilyl- or triethylsilyl cyanide and reaction with olefinic alkylating reagents 7-10 furnishes products 11-16 in high yields.On heating to 180 deg C these products, containing a diene and a dienophilic moiety, undergo in most cases quantitative intramolecular Diels-Alder reactions.Since the cycloadducts can be deprotected under very mild conditions, hexahydro-indenones (22, 25) and -naphthalinones (27, 29) can be synthesized for the first time avoiding isomerisation of the double bond.Intramolecular cycloadditions without protected carbonyl groups in the precursor (19, 21) yield hexahydronaphthalinones (30, 34) with conjugated double bonds exclusively, whereas ring closure to hexahydro-indenones (33) fails.Related examples described in the literature suffer from the same drawback.
- Fischer, Klaus,Huenig, Siegfried
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p. 2590 - 2608
(2007/10/02)
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- Total Synthesis of (+/-)-Nitramine. Development of a Ketene Equivalent in the Ene Reaction
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(+/-)-Nitramine (1a) was synthesized in seven steps from methylenecyclohexane in 33percent overall yield.A three-step sequence was developed from methylenecyclohexane to aldehyde 4 in which methyl α-chloroacrylate was used as a ketene equivalent in the ene reaction.Aldehyde 4 was converted to nitrone 3 which cyclized to a 2.5:1 mixture of 2 and 9.Hydrogenolysis of 2 gave 1a.Lewis acid catalyzed cyclization of 4 gave a 3.5:1 mixture of hydrindanones 13 and 14 at 25 deg C and a 12:1 mixture of 13 and 14 at -20 deg C.
- Snider, Barry B.,Cartaya-Marin, Claudia P.
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p. 1688 - 1691
(2007/10/02)
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- ADDITION OF ORGANIC ACIDS TO cis-BICYCLONONA-3,7-DIENE. SYNTHESIS OF COMPOUNDS OF THE BREXANE AND BRENDANE SERIES
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The esters of cis-bicyclononenols, exo- and endo-brexan-5-ols, and exo-brendan-2-ol were obtained by the addition of formic, acetic, and trifluoroacetic acids to cis-bicyclonona-3,7-diene.The composition of the reaction products and its dependence on the reaction conditions were determined.A method is proposed for the separation of the bicyclic and tricyclic components.The mechanism of the transannular cyclization is discussed.
- Arbuzov, V. A.,Gevorkyan, G. G.,Pekhk, T. I.,Bobyleva, N. A.,Belikova, N. A.
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p. 1114 - 1124
(2007/10/02)
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- Silicon-Directed Nazarov Reactions II. Preparation and Cyclization of β-Silyl-substituted Divinyl Ketones
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Two general methods for the preparation of β-silyl-substituted divinyl ketones have been developed starting from either α,β-unsaturated aldehydes or simple ketones.Anhydrous FeCl3 induces the cyclization to cyclopentenones under mild conditions and in good yields with predictable and complete control over the position of the double bond in the five-membered ring.The observed effects of substituents on rate can be explained by a rate-determining cationic electrocyclization.Silyl substitution has been shown to retard the reaction.
- Jones, Todd K.,Denmark, Scott E.
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p. 2377 - 2396
(2007/10/02)
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- HYDROBORATION AND OXYMERCURATION-DEMERCURATION OF CIS-BICYCLONONA-3,7-DIENE. SYNTHESIS OF CIS-BICYCLONONENONES
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Four isomeric cis-bicyclononenones were obtained from cis-bicyclonona-3,7-diene by hydroboration and oxymercuration-demercuration.Their structures were determined by means of their 13C NMR spectra.The addition of the hydroborating agents takes place preferentially (60-80percent) at the cyclopentene double bond at the C7 and C8 atoms and is most selective in the case of 9-borabicyclononane.The direction of addition of mercuric acetate depends on the solvent; the reaction takes place most selectively (95percent) at the cyclohexene double bond in 1:9 aqueous THF, and here the mercury adds to the C4 carbon atom to the extent of 90percent.
- Arbuzov, V. A.,Pekhk, T. I.,Belikova, N. A.,Bobyleva, A. A.,Plate, A. F.
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p. 273 - 282
(2007/10/02)
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- Stereochemical studies. X. Synthesis of some epimeric δ-lactones
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Stereospecific synthesis are reported for the δ-lactones 3, 5, 8, 17, and 26.
- Cooke, Ellen,Paradellis, Themistocles C.,Edward John T.
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