Regioselectivity of the 1,3-Dipolar Cycloaddition of Organic Azides to 7-Heteronorbornadienes. Synthesis of β-Substituted Furans/Pyrroles

An efficient procedure for the preparation of beta-substituted furans/pyrroles is presented. The methodology is based on the use of 7-oxa/azanorbornadienes as dipolarophiles in 1,3-dipolar cycloaddition with benzyl azide. The triazoline cycloadduct thus formed spontaneously decomposes via a retro-Diels-Alder (rDA) reaction to afford a beta-substituted furan/pyrrole derivative and a stable triazole. The scope of this tandem 1,3-dipolar cycloaddition/rDA reaction was studied with thirteen 7-heteronor-bornadienes. This study allowed a deep knowledge of the regioselectivity of the reaction, which can be tuned through the substituents of the heteronorbornadienic systems.