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Synlett 1994; 1994(7): 509-510
DOI: 10.1055/s-1994-22907
DOI: 10.1055/s-1994-22907
letter
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Inter- and Intramolecular Hetero-Diels-Alder Reactions, Part 48.1 De-Novo Synthesis of Enantiopure Carbohydrates: Preparation of Ethyl β-D- and β-L-Mannopyranosides by an Asymmetrically Induced Hetero Diels-Alder Reaction
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Publikationsverlauf
Publikationsdatum:
18. September 2002 (online)
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The synthesis of dihydropyrans 4 and 5 based on the asymmetrically 1,6-induced intermolecular hetero Diels-Alder reaction of the heterodiene 2 [(4S)-4-tert-Butyl-3-[(E)-4′-benzyloxy-2′-oxo-3′-butenoyl]-oxazolidin-2-one] with (Z)-1-acetoxy-2-ethoxyethene 3 in the presence of a Lewis acid is described. A reversal of facial differentiation could be achieved by variation of the Lewis acid. Thus cycloaddition of 2 and 3 preferentially yields 4 in the presence of Me2AICl and 5 using TMS-OTf. Simple transformations of 4 and 5, respectively afforded the desired ethyl mannopyranosides 12 and ent-12 diastereoselectively and in good yield.