877-01-0Relevant academic research and scientific papers
The crystallographic structure of a Lewis acid-assisted chiral Bronsted acid as an enantioselective protonation reagent for silyl enol ethers
Ishihara, Kazuaki,Nakashima, Daisuke,Hiraiwa, Yukihiro,Yamamoto, Hisashi
, p. 24 - 25 (2003)
It is difficult to control the enantioselectivity in the protonation of silyl enol ethers with simple chiral Bronsted acids, mainly due to bond flexibility between the proton and its chiral counterion, the orientational flexibility of the proton, and the fact that the proton sources available are limited to acidic compounds such as chiral carboxylic acids. To overcome these difficulties, we have developed a Lewis acid-assisted chiral Bronsted acid (LBA) system. The coordination of Lewis acids with Bronsted acids restricts the orientation of protons and increases their acidity. Optically active binaphthol (BINOL) derivative·SnCl4 complexes are very effective as enantioselective protonation reagents for silyl enol ethers. However, their exact structures have not yet been determined. We describe here optically active 1,2-diarylethane-1,2-diol derivative·SnCl4 as a new type of LBA for the enantioselective protonation as well as its crystallographic structure. A variety of optically active 1,2-diarylethane-1,2-diols could be readily prepared by asymmetric syn-dihydroxylation. This is a great advantage over BINOL for the flexible design of a new LBA. The most significant finding is that we were able to specify the conformational direction of the H-O bond of LBA, which has some asymmetric inductivity, by X-ray diffraction analysis. The stereochemical course in the enantioselective protonation of silyl enol ethers using LBA would be controlled by a linear OH/π interaction with an initial step. The absolute stereopreference in enantioselective reactions using BINOL·SnCl4 can also be explained in terms of this uniformly mechanistic interpretation. Copyright
Dynamic enzymatic kinetic resolution of methyl 2,3-dihydro-1h-indene-1- carboxylate
Pietruszka, Joerg,Simon, Robert Christian,Kruska, Fabian,Braun, Manfred
experimental part, p. 6217 - 6224 (2010/03/26)
A new reaction setup for kinetic enzymatic resolution was established and is demonstrated for the case of the hydrolase-catalysed conversion of methyl 2,3-dihydro-1H-indene1-carboxylate (1) in conjunction with a base-catalysed racemisation. The system allows controlled racemisation, resulting in efficient dynamic kinetic resolution (DKR) of the title compound. Short reaction times and high enantio-selectivities were obtained with CAL-B and TBD (1,5,7-triazabicyclo[4,4.0]dec-5-ene). Compound (R)-1 (ee 95%) served as a starting material in a domino reaction that led to the biaryl indanyl ketone (R)-8, a lead compound for novel inhibitors of peptidyl-prolyl-cis/irans- isomerases, in 94 % ee. Wiley-VCH Verlag GmbH & Co. KGaA,.
Chiral benzyllithium compounds: High configurative stability of (R)- and (S)-1-lithioindan-1-yl N,N-diisopropylcarbamate and unexpected stereochemical course of the substitution reactions
Derwing, Christoph,Frank, Holger,Hoppe, Dieter
, p. 3519 - 3524 (2007/10/03)
The title compound, 6, was generated by stereospecific deprotonation of the optically active carbamate 5 with sec-butyllithium/TMEDA and proved to be configuratively completely stable in ethereal solution at -78 °C. Compared with open-chain analogs, the trend for stereoretentive substitution is enhanced. Even the reaction with trialkyltin chlorides leads to partial racemization due to competing front face attack. Semiempirical calculations point to an increased degree of pyramidalization and to a higher barrier for planarization in the cyclic benzyllithium compound, both of which disfavor the rear face attack.
On the Absolute Configuration of (+)-Indane-1-carboxylic Acid
Hansen, Hans-Juergen,Sliwka, Hans-Richard,Hug, Werner
, p. 325 - 343 (2007/10/02)
The (R)-configuration, attributed to (+)-indane-carboxylic acid ((+)-1) by Fredga, is unequivocally confirmed (Scheme 1).Configurational doubts, raised by an erroneous ORD. curve of (-)-1-methylindane ((-)-4) published by Brewster and Buta, are unfounded (cf. the following paper of Brewster and the corrections in ).This was further verified by preparing deuteriated 1-methylindanes starting with (-)-(R)-3-phenylbutyric acid ((-)-(R)-5) as well as with (+)-(R)-1 or (-)-(S)-1 (Scheme 2).The ORD. curves of the optically active 4 thus obtained were (disregarding deuterium isotope effects) identical or antipodal, respectively (cf.Fig.1,2, and 7a-e).Optically active methyl indane-1-carboxylates ((-)-(R)-14 or (+)-(S)--14) show a strong solvent dependence of their ORD. and CD. spectra with a sign inversion occuring in going from isooctane to methanol or benzene.The observed changes can be explained by a change in the population of comformations where the ester carbonyl group is eclipsed either with the C(1),C(2)- or C(1),H-bond, with the n,?*-transition having a slightly different energy and the ester group an essentially enantiomeric environment with respect to its orientation relative to the benzene moiety.
