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Keywords:

  • carbenoids;
  • diazo compounds;
  • medium-ring compounds;
  • rhodium;
  • ylides

Abstract

α-Diazo β-ketoesters and diketones react with cyclic acetals under RhII catalysis to yield unprecedented polyoxygenated 8- and 9-membered rings in one pot. The reactions occur under mild conditions with yields up to 90 %. A perfect regioselectivity is obtained, which can be rationalized through a mechanistic hypothesis that considers 1) the formation of an oxonium ylide, 2) its transformation into an unsaturated acyclic oxocarbenium electrophilic intermediate, and 3) an intramolecular nucleophilic attack in a direct application of Baldwin’s rules.