Carbohydrate-Derived Chiral Furanosidic α,β-Unsaturated Aldehydes in Conjugate and Diels-Alder Addition Reactions. Steric Hindrance by the Anomeric Substituent

• The title aldehydes (lr, 1s, 2, and 3) underwent virtually diastereospecific conjugate addition by lithium methylcyanocuprate. The bulkiness of the anomeric benzyloxy or methoxy groups direct the attacking nucleophile to the less hindered side of the furanosidic ring. The stereochemical outcome of the Diels-Alder additions of cyclopentadiene to lr and 1s was governed almost completely by the bulkiness of the anomeric benzyloxy group, which directed cyclopentadiene to the less hindered side of the furanosidic ring. When an additional substituent was positioned trans to the anomeric substituent (2), a mixture of all four possible diastereomers was obtained. With both substituents on the same side of the ring (3), complete π-facial selectivity was obtained. In both the conjugate and Diels-Alder addition products, NMR data could be used to determine the stereostructures of all diastereomers. Both product types showed oxygen atom induced proton deshielding and carbon shielding effects in NMR.

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

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

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