Double stereodifferentiating Dreiding-Schmidt reactions.
Spiroanellated carbohydrate-derived a-methylene-g-butyrolactones with an addnl. stereogenic center in the b-position of the anellated lactone ring and spiroanellated a-alkylidene-g-butyrolactones, e.g. I and II (R = Me, Et), were obtained in a stereoselective manner by Dreiding-Schmidt reactions of the deoxy-uloside III or of D-erythronolactone IV with the corresponding (Z) alkyl-2-bromomethyl-2-alkenoates, e.g., BrCH2C(CO2OEt):CHR in the presence of the highly reactive zinc-silver/graphite surface compd.
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