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-A lder cycloaddition with a variety of dienophiles to afford ring-opened cycloadducts that are readily dehydrated using BF3 . OEt2 to give pol ysubstituted anilines. In each case, the cycloaddition proceeds with h igh regioselectivity, with the electron-withdrawing group being locate d ortho to the amino group. The most favorable FMO interaction is betw een the HOMO of the furanamine and the LUMO of the dienophile. The ato mic coefficient at the ester carbon of the furan is larger than that a t the amino center, and this nicely accommodates the observed regiosel ectivity. The [4 + 2]-cycloaddition of N-(5-nitrofuranyl)morpholine wi th 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 intermediat e with concomitant migration of the nitro group. The mild reaction con ditions with which furan-2-carbamic acid tert-butyl ester undergoes Di els-Alder cycloaddition with N-phenylmaleimide allow for the ready iso lation of the initial oxybridged cycloadduct.