Applications of the Isomerizations of Highly Strained Molecules to the Synthesis of Heterocycles

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We have found that a variety of bi- and tri-cyclic compounds having a highly strained bicyclopentane, bicycloheptane, or tricycloheptane ring system with one or more heteroatoms (nitrogen, oxygen, sulfur, or phosphorous) readily undergo thermal or photochemical valence isomeriztion with ring opening or rearrangement to give the corresponding novel seven-or eight-membered heterocyclic ring compounds or polycyclic heterocycles, such as azepines, diazepines, oxazepines, thiazepines, benzazepines, benzodiazepines, benzoxepins, benzothiazepines, benzodioxocins, benzazocins, azepino-azepines, pyrrolobenzofurans, pyrido-oxepines, quino-oxepines, and various condensed heterocyclic compounds.These results indicate that such highly strained ring systems, easily prepared from commercially available ring compounds, are new useful synthons for a variety of heterocyclic compounds.Further synthetic applications of these results to other highly strained ring systems are under investigation.