文摘
Rh(II)-catalyzed oxonium ylide formation鈥揫2,3] sigmatropic rearrangement of 伪-diazo-尾-ketoesters possessing 纬-cyclic unsaturated acetal substitution, followed by acid-catalyzed elimination鈥搇actonization, provides a concise approach to 1,7-dioxaspiro[4.4]non-2-ene-4,6-diones. The process creates adjacent quaternary stereocenters with full control of the relative stereochemistry. An unsymmetrical monomethylated cyclic unsaturated acetal leads to hyperolactone C, where ylide formation鈥搑earrangement proceeds with high selectivity between subtly nonequivalent acetal oxygen atoms.