Alcohol Substrate (alcohol + substrate)

Distribution by Scientific Domains


Selected Abstracts


Gold- and Silver-Catalyzed Tandem Amination/Ring Expansion of Cyclopropyl Methanols with Sulfonamides as an Expedient Route to Pyrrolidines

CHEMISTRY - A EUROPEAN JOURNAL, Issue 33 2008
Weidong Rao
Abstract An efficient synthetic route to pyrrolidines that relies on AuCl/AgOTf-catalyzed tandem amination/ring expansion of substituted cyclopropyl methanols with sulfonamides is reported herein. The reactions proceed rapidly at 100,°C with catalyst loadings as low as 2,mol,% and produce the pyrrolidine products in yields of 30,95,%. The method was shown to be applicable to a broad range of cyclopropyl methanols, including unactivated ones, and sulfonamide substrates containing electron-withdrawing, electron-donating, and sterically-demanding substituents. The mechanism is suggested to involve activation of the alcohol substrate by the AuCl/AgOTf catalyst, followed by ionization of the starting material, which causes ring opening of the cyclopropane moiety and trapping by the sulfonamide nucleophile. The resultant aminated acyclic intermediate undergoes subsequent intramolecular hydroamination to give the pyrrolidine. [source]


The DMAP-Catalyzed Acetylation of Alcohols,A Mechanistic Study (DMAP=4-(Dimethylamino)pyridine)

CHEMISTRY - A EUROPEAN JOURNAL, Issue 16 2005
Shangjie Xu Dr.
Abstract The acetylation of tert -butanol with acetic anhydride catalyzed by 4-(dimethylamino)pyridine (DMAP) has been studied at the Becke3,LYP/6-311+G(d,p)//Becke3,LYP/6-31G(d) level of theory. Solvent effects have been estimated through single-point calculations with the PCM/UAHF solvation model. The energetically most favorable pathway proceeds through nucleophilic attack of DMAP at the anhydride carbonyl group and subsequent formation of the corresponding acetylpyridinium/acetate ion pair. Reaction of this ion pair with the alcohol substrate yields the final product, tert -butylacetate. The competing base-catalyzed reaction pathway can either proceed in a concerted or in a stepwise manner. In both cases the reaction barrier far exceeds that of the nucleophilic catalysis mechanism. The reaction mechanism has also been studied experimentally in dichloromethane through analysis of the reaction kinetics for the acetylation of cyclohexanol with acetic anhydride, in the presence of DMAP as catalyst and triethylamine as the auxiliary base. The reaction is found to be first-order with respect to acetic anhydride, cyclohexanol, and DMAP, and zero-order with respect to triethyl amine. Both the theoretical as well as the experimental studies strongly support the nucleophilic catalysis pathway. [source]


Borrowing Hydrogen: Indirect "Wittig" Olefination for the Formation of C,C Bonds from Alcohols

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 19 2006
Phillip J. Black
Abstract The successful development of an indirect three-step domino sequence for the formation of C,C bonds from alcohol substrates is described. An iridium-catalysed dehydrogenation of alcohol 1 affords the intermediate aldehyde 2. The desired C,C bond can then be formed by a facile Wittig olefination, yielding the intermediate alkene 3. In the final step the alkene is hydrogenated to afford the indirect Wittig product, the alkane 4. The key to this process is the concept of borrowing hydrogen; hydrogen removed in the initial dehydrogenation step is simply borrowed by the iridium catalyst. Functioning as a hydrogen reservoir, the catalyst facilitates C,C bond formation before subsequently returning the borrowed hydrogen in the final step. Herein we present full details of our examination into both the substrate and reaction scope and the limitations of the catalytic cycle. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Site-directed mutagenesis of selected residues at the active site of aryl-alcohol oxidase, an H2O2 -producing ligninolytic enzyme

FEBS JOURNAL, Issue 21 2006
Patricia Ferreira
Aryl-alcohol oxidase provides H2O2 for lignin biodegradation, a key process for carbon recycling in land ecosystems that is also of great biotechnological interest. However, little is known of the structural determinants of the catalytic activity of this fungal flavoenzyme, which oxidizes a variety of polyunsaturated alcohols. Different alcohol substrates were docked on the aryl-alcohol oxidase molecular structure, and six amino acid residues surrounding the putative substrate-binding site were chosen for site-directed mutagenesis modification. Several Pleurotus eryngii aryl-alcohol oxidase variants were purified to homogeneity after heterologous expression in Emericella nidulans, and characterized in terms of their steady-state kinetic properties. Two histidine residues (His502 and His546) are strictly required for aryl-alcohol oxidase catalysis, as shown by the lack of activity of different variants. This fact, together with their location near the isoalloxazine ring of FAD, suggested a contribution to catalysis by alcohol activation, enabling its oxidation by flavin-adenine dinucleotide (FAD). The presence of two aromatic residues (at positions 92 and 501) is also required, as shown by the conserved activity of the Y92F and F501Y enzyme variants and the strongly impaired activity of Y92A and F501A. By contrast, a third aromatic residue (Tyr78) does not seem to be involved in catalysis. The kinetic and spectral properties of the Phe501 variants suggested that this residue could affect the FAD environment, modulating the catalytic rate of the enzyme. Finaly, L315 affects the enzyme kcat, although it is not located in the near vicinity of the cofactor. The present study provides the first evidence for the role of aryl-alcohol oxidase active site residues. [source]