title: Reactions in the conjugated 'ene-ene-yne' manifold: five-membered ring fragmentation and ring formation via coarctate/pseudocoarctate mechanisms.
abstract: The fragmentation of a 5-membered heteroaromatic ring to afford a conjugated ene-ene-yne skeleton, and the corresponding reverse process, cyclization of the hetero-ene-ene-yne motif to generate a variety of heterocyclic systems, are the subject of this review. These synthetically useful reactions, which proceed through a coarctate/pseudocoarctate mechanistic pathway, are unique in that they involve the generation of either a carbene or nitrene intermediate, and provide access to hard to obtain heterocyclic or ene-ene-yne structures. While fragmentation of heteroaromatic rings containing a exocyclic carbene or nitrene has been well documented in the literature for over 40 years, the use of hetero-ene-ene-yne precursors to synthesize heterocycles is a relatively new approach that is generating much interest in the literature. This review highlights both the synthetic and mechanistic aspects of these unique reactions.
authors.affiliation: Department of Chemistry, University of Oregon, Eugene, Oregon 97403-1253, USA.
authors.forename: Laura D
authors.initials: LD
authors.lastname: Shirtcliff
authors.forename: Sean P
authors.initials: SP
authors.lastname: McClintock
authors.forename: Michael M
authors.initials: MM
authors.lastname: Haley