Reactions of aminobenzoic acids with α,β-acetylenic γ-hydroxy nitriles: synthesis of functionalized amino acids and unusually facile esterification and acetylene hydration

2-Aminobenzoic acid 1 reacts with α,β-acetylenic γ-hydroxy nitriles 4 and 5 to afford 2-[(5-iminio-2,2-dialkyl-2,5-dihydro-3-furanyl)amino]benzenecarboxylates 7 and 8 (yield 73–74%), a new class of unnatural amino acids in a peculiar zwitterionic form, having the positive charge transferred to the remote imino group of the dihydrofuranyl substituent. 3- and 4-Aminobenzoic acids 2 and 3 with α,β-acetylenic γ-hydroxy nitriles 4–6 undergo entirely different transformations to deliver the esters of cyanomethylhydroxyalkyl ketones 9–12, which result from the unusually facile esterification of the hydroxyl function and simultaneous hydration of the triple bond. 4-Aminobenzoic acid 3 is found to be an active organic catalyst for the one-pot conversion of α,β-acetylenic γ-hydroxy nitrile 4 to 5-amino-2,2-dimethyl-3(2H)-furanone 13, in 80% yield.