Regiodivergent dipolar cycloaddition based on pyrrole-2,3-diones

Abstract

It was previously demonstrated, that thermal decarbonylation of N-substituted 2,3-dihydro-2,3-pyrroldiones afforded imidoylketenes, whose chemical behavior largely depends on the nature of substituents at N-1. It was discovered that N-(diphenylenamino)pyrrolediones experienced facile CO-extrusion at elevated temperatures and the resulting a zwitterionic dihydropyrazolone species, which can be represented by enolate-iminium 1,4-dipole resonance form. In the absence of dipolarophiles, the products of [4+4]-cyclodimerization – bis(pyrazolo)dioxadiazocines – were formed in high yields. To this end, we generated the ketenes in the presence of alkyl vinyl ethers, aldehydes, ketenes, nitriles and isocyanides targeting products of dipolar cycloadditions. We further elaborated on the development of various synthetic schemes involving cycloaddition of these unusual 1,4-dipoles. Dipyrazolodioxadiazocines are shelf-stable "ready-to-use" precursors for an in situ generation of enolate-iminium 1,4-dipoles.