Coordination Of Lewis Acid Research Articles

Asymmetric synthesis of functionalized tertiary homoallyl alcohols by diastereoselective allylation of chiral .alpha.-keto amides derived from (S)-proline esters: control of stereochemistry based on saturated coordination of Lewis acid

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAsymmetric synthesis of functionalized tertiary homoallyl alcohols by diastereoselective allylation of chiral .alpha.-keto amides derived from (S)-proline esters: control of stereochemistry based on saturated coordination of Lewis acidKenso Soai and Miyuki IshizakiCite this: J. Org. Chem. 1986, 51, 17, 3290–3295Publication Date (Print):August 1, 1986Publication History Published online1 May 2002Published inissue 1 August 1986https://doi.org/10.1021/jo00367a008RIGHTS & PERMISSIONSArticle Views395Altmetric-Citations35LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (801 KB) Get e-Alerts Get e-Alerts

Ｈｙｐｅｒｖａｌｅｎｔ有機よう素化合物を活用する有機合成 けい素，すず化合物との反応

Iodosylbenzene activated by the coordination of Lewis acids to the oxygen atom reacts readily with a variety of organosilicon and tin compounds to produce the hypervalent organoiodine (III) species. Allyl- and vinyliodine (III) compounds are highly reactive and act as the species equivalent to allyl and vinyl cations, because iodine (III) at the hypervalent state is a good Ieaving group. Reaction of alkynyliodine (III) compounds with stable enolates of 1, 3-dicarbonyl compounds produces substituted cyclopentenes via the (1, 5) C-H insertion of alkylidene carbene intermediates. 1, 4-Fragmentation of γ-tributylstannyl alcohols using iodosylbenzene, BF3, and DCC gives rise to unsaturated carbonyl compounds. The fragmentation, combined with conjugated addition of Bu3SnLi and reduction or alkylation, offers an efficient procedure for the reductive and alkylative ring opening of cyclic vinyl ketones.

Surface-enhanced raman scattering study on the structure of 2,2′-bipyridine adsorbed on an Ag electrode

The surface-enhanced Raman scattering (SERS) spectra were measured for 5 m M 2,2′-bipyridine+0.1 M KX (X = CI, Br or I) and the assignments of the bands were discussed by comparing the surface spectra with the Raman and infrared spectra of Ag(I)(bpy) 2NO 3 and bpy itself. As the electrode potential was changed from +0.05 to −1.1 V (vs. Ag/AgCl), the SERS spectra showed a sequence of changes in their features indicating that a series of transformations are taking place between at least four kinds of molecular states (Type I, II, III and IV) of adsorbed bpy molecules on silver electrode surfaces. Near +0.05 V in the KCI electrolyte solution the adsorbates take on a structure of type I which gives a SERS spectrum almost identical with the Raman spectrum of Ag(I)(bpy) 2NO 3. A study of the effect of illumination by a 514.5 nm laser indicated that the type I adsorbate is a reaction product from bpy molecules and Ag atoms which were created by photoreduction of an AgCl layer produced during the anodization process of the electrode. When the electrode potential was changed to a more negative region (−0.2, −0.4 and −0.5 V for the KCl, KBr and KI electrolytes, respectively), the silver halide layers were electrochemically reduced forming a fresh Ag layer. On adsorbing on this layer the bpy molecules always assume a structure of type II, where the molecules again take on coordination and backbone structures similar to those of the argentous complex. In this state some of the out-of-plane vibrations of the pyridine moieties are observed to be specifically enhanced, which suggests that the molecular plane of the ligands lies almost flat on the electrode surface. On sweeping the electrode potential to more negative values, the type II adsorbate is generally converted to a type III species, which is characterized by its breathing vibration observed at 1025 cm −1. It was suggested that in this state the nitrogen atoms of the pyridine moieties are strongly chemisorbed to a silver atom on the electrode surface, forming a Lewis acid coordination structure. In the KCl and KBr electrolyte solutions the type III species is converted to a type IV adsorbate when the electrode potential approaches the pzc of the Ag electrode (about −0.91 V). In the latter species the adsorbed bpy molecules give rise to the breathing vibration near 1005 cm −1 suggesting that the molecules exist in a physisorbed state.

Infrared study of surface species arising from ammonia adsorption on oxide surfaces

Infrared spectra of ammonia adsorbed on CoO, NiO, SiO 2, CaO, MgO, ZrO 2, ZnO, TiO 2, BeO and Al 2O 3, have been studied in the NH stretching and bending vibration regions at various stages of sample dehydroxylation. Several types of adsorption were found: hydrogen bonding to surface oxygen atoms or hydroxyl groups, coordination to Lewis acid sites and coordination plus hydrogen bonding; on some oxides ammonia molecules dissociate to produce surface NH 2 and OH groups. Frequencies characteristic of the distinct adsorbed species were determined. Except for Al 2O 3, no evidence was found for Brönsted acid sites on the surface of the above oxides.

Torsional strain considerations in the mechanism of the proteolytic enzymes, with particular application to carboxypeptidase A

Torsional deformation of the peptide linkage by anti distortion of cis substituents (i.e., forcing groups attached to one side of an amide partial π bond out of plane in opposite directions) leads to rehybridization of the constituent atoms (nitrogen and carbonyl carbon) toward tetrahedral geometry. In consequence the partial π bond is uniquely activated toward trans (antarafacial) addition with defined steric orientation of addends. Application of these considerations to the known structure of an enzyme-substrate complex of carboxypeptidase A leads to a unique mechanistic hypothesis for proteolytic cleavage by this enzyme. Extant evidence concerning the mode of catalysis is considered in light of a mechanism involving electrostatically induced torsional activation of the scissile peptide bond, Lewis acid coordination of zinc to amide carbonyl, proton donation from Glu 270 to the amide nitrogen of the scissile bond, with concerted attack upon the amide carbonyl by solvent water.