Novel [12 + 2] Cycloaddition of 2H-4,9-Methanocyclo-Undeca[b]Furan-2-Ones with Enamines: Synthesis and Properties of 4,9-Methanocyclopentacycloundecenes and a Benzo-Annulated Derivative

摘要

Novel cycloaddition reactions of 2H-4,9-methanocycloundeca[b]furan-2-one and 3-chloro-substituted derivative with enamines underwant novel [12 + 2] cycloaddition reaction followed by decarboxylation and elimination of amine to give 4,9-methanocyclopentacycloundecene derivatives in modest yields. Upon treatment of DDQ, cyclohexane-annulated 5-chloro-4,9-methanocyclopentacyclo-undecene was dehydrogenated easily to give the first example of a benzo-annulated 4,9-methanocyclopenacycloundecene ring system. Chemical as well as spectroscopic properties of them were studied, and it was clarified that benzo-annulation causes an appreciable degree of bond alternation and reduced ring current.