Transferring Substituents from Alkynes to Furans and Pyrroles through Heteronorbornadienes as Intermediates: Synthesis of β-Substituted Pyrroles/Furans.

The use of 7-oxa/azanorbornadienes as synthetic intermediates for the preparation of 3/4-substituted (β-substituted) furans/pyrroles is presented. The method lies in the inverse electron demand Diels-Alder (iEDDA) cycloaddition between a substituted heteronorbornadiene and an electron-poor tetrazine followed by spontaneous fragmentation of the resulting cycloadduct via two retro-Diels-Alder (rDA) reactions affording a β-substituted furan/pyrrole. The scope of this tandem iEDDA/rDA/rDA reaction was explored in the preparation of 29 heterocycles. A one-pot procedure starting directly from the alkyne precursors of the heteronorbornadiene intermediates is also described.