DBU-Catalyzed Ring Expansion or Ene-amine Formation Involving δ-Acetoxy Allenoates and <i>N</i>-Sulfonyl Hydrazides

Abstract

DBU-catalyzed spiro-annulation and concomitant ring expansion/domino reaction of δ-acetoxy allenoates with cycl-2-ene-<i>N</i>-sulfonyl hydrazides afford ring-expanded (5 → 6, 6 → 7, and 7 → 8) products. By contrast, cycl-3-ene/ane-<i>N</i>-sulfonyl hydrazones under similar conditions deliver pyrazole cores with the same allenoate that involves allylic elimination in which δ-acetoxy allenoate serves as 3C-synthon. The key spirocyclic intermediates, as well as dienyl-amine intermediates, are isolated and characterized. An extension to (<i>R</i>)-(-)-carvone-derived sulfonyl hydrazide also led to ring expansion and gave pyrazoloazepine.