Synthesis of Diels-Alder adducts of N-arylmaleimides by a multicomponent reaction between maleic anhydride, dienes, and anilines

We have carried out the synthesis and characterization of some hexahydroisoindolyl benzoic acids and their corresponding ethyl esters by a multicomponent reaction (MCR) between aminobenzoic acids or aminobenzoates, maleic anhydride, and isoprene in the absence of catalysts. According to additional experiments, theMCR takes place by sequential formation of N-arylmaleamic acids from the aminobenzoic acids or aminobenzoates and maleic anhydride, Diels-Alder adducts of the acids and isoprene, and finally the imides. The ¹H NMR data (coupling constants) of the adducts suggested that the preferred conformation of the corresponding cyclohexene rings is a syn-boat, a fact supported by a density functional theory (DFT) conformational analysis and DFT calculations of the spin-spin coupling constants of the corresponding conformers. OurMCR synthetic methodology was tested successfully in the synthesis of other adducts, for which cyclopentadiene and other anilines were employed.