Anomeric Effect in Furanosides. Experimental Evidence from Conformationally Restricted Compounds

• A series of conformationally restricted 0-, C-, S-, and N-“furanosides” have been synthesized, where the number 3 and 4 carbons are part of a norbornane ring system. All the carbons of the tetrahydrofuran ring are kept in one plane by the rigid norbornane skeleton, permitting only the ring oxygen to move above or below the tetrahydrofuran ring plane. This causes the substituents on carbon 2 to occupy a pseudoaxial or a pseudoequatorial position. The “norbornane-furanosides” were investigated by NMR, X-ray crystallography, and molecular mechanics calculations. The O-and S-furanosides preferred the conformation with a pseudoaxial anomeric substituent, whereas its C-furanosidic counterpart preferred the conformation with a pseudoequatorial substituent. These findings constitute the first demonstration of a “by definition” anomeric effect in furanosides. © 1994, American Chemical Society. All rights reserved.

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NATURVETENSKAP  -- Kemi -- Organisk kemi (hsv//swe)

NATURAL SCIENCES  -- Chemical Sciences -- Organic Chemistry (hsv//eng)

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