Diels-Alder reaction of 2-amino-substituted furans as a method for preparing substituted anilines

5-Amino-2-furancarboxylic acid methyl ester undergoes a facile Diels-Alder cycloaddition with a variety of dienophiles to afford ring-opened cycloadducts that are readily dehydrated using BF3 . OEt2 to give polysubstituted anilines. In each case, the cycloaddition proceeds with high regioselectivity, with the electron-withdrawing group being located ortho to the amino group. The most favorable FMO interaction is between the HOMO of the furanamine and the LUMO of the dienophile. The atomic coefficient at the ester carbon of the furan is larger than that at the amino center, and this nicely accommodates the observed regioselectivity. The [4 + 2]-cycloaddition of N-(5-nitrofuranyl)morpholine with methyl vinyl ketone affords a mixture of three phenols. One of the phenols is derived from a Diels-Alder reaction followed by nitro group ejection and subsequent aromatization. The remaining two phenols are the result of cleavage of the initially formed oxabicyclic intermediate with concomitant migration of the nitro group. The mild reaction conditions with which furan-2-carbamic acid tert-butyl ester undergoes Diels-Alder cycloaddition with N-phenylmaleimide allow for the ready isolation of the initial oxybridged cycloadduct.