Expedient reaction sequences have been developed to convert o-fructose into a diverse collection of spirocyclic dihydropyrandiols with 2S,3S (10, ll), 2R,5S (17, 18), and 2S,3R configuration (19), and of dihydropyranones 4 -7 with 2 s and 2R chirality. Due to the rigid attachment of pyranoid and dioxolane rings around a chiral spiro carbon which is to result in foreseeable regioand stereo-selectivities on additions to the olefinic and/or carbonyl double bonds, they represent highly versatile six-carbon synthons. -Key intermediates for their obtention are the long-known 3-O-benzoyl(8) and 3-0-tosyl derivatives (12) of 1,2-0-isopropylidene-~-fructopyranose, as well as the novel 4,5-di-Omesyl (9), the 3,4-di-O-tosyl (15), and the 3,4-di-O-benzoyl analogs 23. Introduction of olefinic unsaturation was effected with iodidelzinc in refluxing DMF (TipsonCohen procedure) or with triphenylphosphane/iodine/imidazole reagents, carbonyl groups were generated ilia PCC oxidation of the respective alcohols. The utilization of D-fructose as chiral source for the construction of complex, non-carbohydrate natural products in enantiomerically pure form is essentially negligible, recent accounts of the use of sugars as chiral substrates not even containing one example*). Only investigations towards the total synthesis of thermozymocidin3) and some pheromone-related spirobidioxanes4) have made use of o-fructose as starting material. This is undoubtedly due to the fact that the chemistry of fructose5) is less developed than that of the common aldoses which, in turn, has its cause in the adoption of all possible tautorneric forms in solution" and, hence, in product mixtures on reactions. Accordingly, the number of readily accessible, simple derivatives in a fixed tautomeric form is comparatively small: the tetraacetate7s*) and tetrabenzoate8) of 6-chloro-6-VCH Verlagsgesellschaft mbH, D-6940 Weinheim, 1985
