0000000000480751
AUTHOR
Karl Heinz Dötz
Synthesis of Hydroquinoid C- and O-Biphenyl Disaccharides by Chromium-Templated Benzannulation Reactions
Organometallic monosaccharides 6−10 containing a chromium styrylcarbene skeleton have been synthesized in quantitative yield from O-glycoside methylcarbene complexes 1−5 bearing diisopropylidene-protected glucose, mannose, galactose, or fructose in a trans-selective aldol condensation with benzaldehyde. These compounds undergo a chromium-templated benzannulation upon reaction with ethynyl glucoside to give diastereoisomeric mixtures of Cr(CO)3 complexes. The differences in their thermodynamic stability was exploited in a diastereoselective synthesis of hydroquinoid biphenyl disaccharides 12−16 in 67−88% yields. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)
Reaction of complex ligands: Part 95. Chromium tricarbonyl complexes of polysubstituted naphthohydroquinones: regioselective synthesis via [3+2+1]-benzannulation and haptotropic rearrangement
Abstract A series of polysubstituted naphthohydroquinoid tricarbonyl chromium complexes were prepared by chromium mediated [3+2+1]-benzannulation of Fischer-type carbene complexes with alkynes. The kinetics and the thermodynamic data of the η6-η6-haptotropic rearrangements were investigated by in-situ NMR spectroscopy. The free activation energies ΔG# range from 23 to 26 kcal mol−1 and only slightly depend on the bulk and the donor/acceptor properties of the substituents. Equilibrium of metal migration was observed for naphthohydroquinone complexes bearing methoxy substituents at the non-hyroquinoid ring (ring A). In complexes bearing methyl groups or only hydrogen substituents at ring A th…
Novel [6]- and [7]Helicene-Like Quinones via Mono- and Bidirectional Chromium-Templated Benzannulation of Bridged Binaphthyl Carbene Complexes
A new organometallic approach to novel, functionalised, helicene-like quinones and bisquinones has been developed based on the chromium-templated [3+2+1] benzannulation reaction. The [5]helicene-analogous monocarbene chromium complexes 4, 5, 17 and 19, derived from dibromo-substituted methylene- or silylene-tethered binaphthols 2 and 3, react with various alkynes to give [6]helicene-like quinones 6–13 and 20–29 after oxidative work-up. A rare competition of angular vs. linear annulation is observed for the incorporation of phenylacetylene that affords quinones 21/22 and 28/29. Protection of the phenolic benzannulation product with camphanic acid chloride 14, followed by chromatographic sepa…