| Abstract
| - The intermolecular [3 + 2] cycloaddition of carbohydrate-derived 1,2-diaza-1,3-butadienes and 1,3-thiazolium-4-olates provides a conceptual basis for the problem of diastereofacial preference in theacyclic series of unsaturated sugars. Experimental results employing a side chain of d-arabinoconfiguration have shown the stereodifferentiation exerted by the first stereogenic center thatrenders the Re,Re face of the acyclic sugar-chain azadiene eligible for cycloaddition (J. Org. Chem.2000, 65, 5089). The results of the present work, now utilizing an alternative framework of d-lyxoconfiguration, evidence the discriminating power of the second stereogenic carbon, which inducesthe preferential approach to the Re,Si face of the heterocyclic dipole. This scheme of face selectivityis also grounded in theoretical calculations at a semiempirical level. In addition to dihydrothiophenes, which are the expected products of the [3 + 2] cycloaddition, bicyclic systems basedon dihydrothieno[2,3-c]piperidine skeleton can also be obtained.
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