Taming the Silylium Ion for Low-Temperature Diels-Alder Reactions
作者:Hendrik F. T. Klare、Klaus Bergander、Martin Oestreich
DOI:10.1002/anie.200904520
日期:2009.11.16
trivalent silicon cation stabilized by an electron‐rich transition metal as the “hot” Lewis acidic site catalyzes challenging Diels–Alderreactions at low temperatures with excellent reaction rates and selectivities (see scheme). In addition to the chemical stability of the silyliumion catalyst (in CH2Cl2), the potential of these reactive compounds is also discussed.
OPLS3 force field. The use of the auxiliary group in the alkylation of appended esters proved disappointing. Diels-Alder cycloaddition of an acrylate, derived from the auxiliary group, with cyclohexadiene furnished a mixture of diastereomeric adducts in essentially equal amounts. The adducts were separated and the corresponding enantiomeric residues were isolated with good enantiomeric excess. Evidence
A step toward polytwistane: synthesis and characterization of C<sub>2</sub>-symmetric tritwistane
作者:Martin Olbrich、Peter Mayer、Dirk Trauner
DOI:10.1039/c3ob42152j
日期:——
Twistane is a classic hydrocarbon with fascinating stereochemical properties. Herein we describe a series of oligomers of twistane that converges on a chiral nanorod, which we term polytwistane. A member of this series, C2-symmetric tritwistane, has been synthesized for the first time.
Silica and alumina modified by Lewis acids as catalysts in Diels-Alder reactions of carbonyl-containing dienophiles
作者:Carlos Cativiela、José M. Fraile、José I. García、José A. Mayoral、Elisabet Pires、Ana J. Royo、François Figueras、Louis C. de Ménorval
DOI:10.1016/s0040-4020(01)89919-1
日期:1993.5
contain strong Lewis acids sites and are efficient catalysts in Diels-Alderreactions of carbonyl-containing dienophiles. In cyclopentadiene reactions, high conversions and endo/exo selectivities are obtained in short reaction times, without excess of diene and with a small amount of catalyst at room temperature. With less reactive dienes, temperature, diene proportion and reaction times must be increased
A norbornene-based sulfide stabilized silyliumion 4 has been synthesized. The S–Si interaction was studied in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis as well as DFT calculations. Unlike the previously reported phosphine-stabilized silyliumion VII, behaving as a Lewis pair, calculations predict that 4 should behave as a Lewis acid toward acrylate derivatives