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)