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Synthetic Scope (synthetic + scope)
Selected AbstractsBroadening the Synthetic Scope of the Iron(III)-Catalyzed Aza-Prins CyclizationEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2010Rubén M. Carballo Abstract The nature and influence of the N -sulfonyl group in aza-Prins cyclization and the reactivity of the six-membered aza-cycle generated has been studied. The aza-Prins cyclization of ,,,-unsaturated amines with a tosyl group at the nitrogen atom produces 2-alkyl-4-halo-1-tosyl-1,2,5,6-tetrahydropyridines with a halovinyl function, extraordinarily stable to further derivatization and detosylation conditions. To modulate the reactivity of such aza-cycles, a general study of the aza-Prins cyclization reaction was performed with several sulfonamides. Ring formation occurs satisfactorily with both N -nosyl and N -mesylamines providing optimal conditions for further synthetic transformations. To exemplify the scope of this methodology, a short synthesis of the alkaloid coniine was successfully carried out. [source] Rhodium-Catalyzed Intermolecular Chelation Controlled Alkene and Alkyne Hydroacylation: Synthetic Scope of ,-S-Substituted Aldehyde Substrates.CHEMINFORM, Issue 47 2006Michael C. Willis Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF. [source] Palladium Pincer Complex Catalyzed Stannyl and Silyl Transfer to Propargylic Substrates: Synthetic Scope and Mechanism.CHEMINFORM, Issue 25 2005Johan Kjellgren Abstract For Abstract see ChemInform Abstract in Full Text. [source] The "Borrowing Hydrogen Strategy" by Supported Ruthenium Hydroxide Catalysts: Synthetic Scope of Symmetrically and Unsymmetrically Substituted AminesCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2010Kazuya Yamaguchi Dr. Abstract The N -alkylation of ammonia (or its surrogates, such as urea, NH4HCO3, and (NH4)2CO3) and amines with alcohols, including primary and secondary alcohols, was efficiently promoted under anaerobic conditions by the easily prepared and inexpensive supported ruthenium hydroxide catalyst Ru(OH)x/TiO2. Various types of symmetrically and unsymmetrically substituted "tertiary" amines could be synthesized by the N -alkylation of ammonia (or its surrogates) and amines with "primary" alcohols. On the other hand, the N -alkylation of ammonia surrogates (i.e., urea and NH4HCO3) with "secondary" alcohols selectively produced the corresponding symmetrically substituted "secondary" amines, even in the presence of excess amounts of alcohols, which is likely due to the steric hindrance of the secondary alcohols and/or secondary amines produced. Under aerobic conditions, nitriles could be synthesized directly from alcohols and ammonia surrogates. The observed catalysis for the present N -alkylation reactions was intrinsically heterogeneous, and the retrieved catalyst could be reused without any significant loss of catalytic performance. The present catalytic transformation would proceed through consecutive N -alkylation reactions, in which alcohols act as alkylating reagents. On the basis of deuterium-labeling experiments, the formation of the ruthenium dihydride species is suggested during the N -alkylation reactions. [source] Synthetic Scope of Alcohol Transfer Dehydrogenation Catalyzed by Cu/Al2O3: A New Metallic Catalyst with Unusual SelectivityCHEMISTRY - A EUROPEAN JOURNAL, Issue 24 2006Federica Zaccheria Dr. Abstract A method for the anaerobic oxidation of a wide series of alcohols including cyclohexanols and steroidal alcohols, has been set up. It relies on a transfer dehydrogenation reaction from the substrate alcohol to styrene catalyzed by a heterogeneous, reusable copper catalyst under very mild liquid-phase experimental conditions (90,°C, N2) and shows unusual selectivity. Thus, the method is selective for the oxidation of secondary and allylic alcohols even in the presence of unprotected primary and benzylic alcohols. Electronic effects and the choice of the hydrogen acceptor account for the selectivity observed. [source] Synthetic Scope and Mechanistic Studies of Ru(OH)x/Al2O3 -Catalyzed Heterogeneous Hydrogen-Transfer ReactionsCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2005Kazuya Yamaguchi Dr. Abstract Three kinds of hydrogen-transfer reactions, namely racemization of chiral secondary alcohols, reduction of carbonyl compounds to alcohols using 2-propanol as a hydrogen donor, and isomerization of allylic alcohols to saturated ketones, are efficiently promoted by the easily prepared and inexpensive supported ruthenium catalyst Ru(OH)x/Al2O3. A wide variety of substrates, such as aromatic, aliphatic, and heterocyclic alcohols or carbonyl compounds, can be converted into the desired products, under anaerobic conditions, in moderate to excellent yields and without the need for additives such as bases. A larger scale, solvent-free reaction is also demonstrated: the isomerization of 1-octen-3-ol with a substrate/catalyst ratio of 20,000/1 shows a very high turnover frequency (TOF) of 18,400 h,1, with a turnover number (TON) that reaches 17,200. The catalysis for these reactions is intrinsically heterogeneous in nature, and the Ru(OH)x/Al2O3 recovered after the reactions can be reused without appreciable loss of catalytic performance. The reaction mechanism of the present Ru(OH)x/Al2O3 -catalyzed hydrogen-transfer reactions were examined with monodeuterated substrates. After the racemization of (S)-1-deuterio-1-phenylethanol in the presence of acetophenone was complete, the deuterium content at the ,-position of the corresponding racemic alcohol was 91,%, whereas no deuterium was incorporated into the ,-position during the racemization of (S)-1-phenylethanol-OD. These results show that direct carbon-to-carbon hydrogen transfer occurs via a metal monohydride for the racemization of chiral secondary alcohols and reduction of carbonyl compounds to alcohols. For the isomerization, the ,-deuterium of 3-deuterio-1-octen-3-ol was selectively relocated at the ,-position of the corresponding ketones (99,% D at the ,-position), suggesting the involvement of a 1,4-addition of ruthenium monohydride species to the ,,,-unsaturated ketone intermediate. The ruthenium monohydride species and the ,,,-unsaturated ketone would be formed through alcoholate formation/,-elimination. Kinetic studies and kinetic isotope effects show that the RuH bond cleavage (hydride transfer) is included in the rate-determining step. [source] Superacid-Catalyzed Dimerization/Cyclization of Isopropenyl-PAHs , Novel Pathways to PAH Dimers, Phenalenes and Their Stable CarbocationsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 21 2008Cédric Brulé Abstract The isopropenyl derivatives of representative classes of polycyclic aromatic hydrocarbons (PAHs) having four and five fused-ring systems, namely pyrene, chrysene, benzo[c]phenanthrene (BcPh), dibenzo[a,c]anthracene (benzo[f]tetraphene) and perylene, were synthesized by Wittig olefination from the corresponding acetyl-PAHs. Under the influence of triflic acid (TfOH), the isopropenyl derivatives were converted to novel PAH dimers and/or phenalenes in a simple one-pot procedure. A plausible mechanism for this process has been outlined, and the synthetic scope of this chemistry has been explored. Structural features in the PAH dimers were examined by DFT. As representative initial and final carbocation intermediates in the reaction sequence, stable carbocations derived from 3-isopropenylperylene and from 4,6,6-trimethyl-6H -dibenzo[a,kl]anthracene were generated and studied directly by NMR spectroscopy. The NMR characteristics and charge delocalization modes in the resulting benzylic carbocations are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Allylation of Aldehyde and Imine Substrates with In Situ Generated Allylboronates , A Simple Route to Enatioenriched Homoallyl AlcoholsEUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 12 2005Sara Sebelius Abstract Allylation of aldehyde and imine substrates was achieved using easily available allylacetates and diboronate reagents in the presence of catalytic amounts of palladium. This operationally simple one-pot reaction has a broad synthetic scope, as many functionalities including, acetate, carbethoxy, amido and nitro groups are tolerated. The allylation reactions proceed with excellent regio- and stereoselectivity affording the branched allylic isomer. By employment of commercially available chiral diboronates enantioenriched homoallyl alcohols (up to 53,% ee) could be obtained. The mechanistic studies revealed that the in situ generated allylboronates react directly with the aldehyde substrates, however the allylation of the sulfonylimine substrate requires palladium catalysis. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | ||||||||||