3H-Pyrroles as a platform for the catalyst-free construction of dihydropyrrolo[2,1-b]oxazoles: [4+2]-cycloaddition vs [2+3]-annulation with 1-cyano-3-hydroxyalkynes

Non-aromatic pyrrole isomers, 3,3-dialkyl-2-aryl-3H-pyrroles, were reacted with 1-cyano-3-hydroxyalkynes under mild, catalyst-free conditions (20-60 degrees C) to regio- and stereoselectively afford (Z)-2(dihydropyrrolo[2,1-b]oxazolylidene)acetonitriles in 62-82% yield, thus evidencing the preference for [2 + 3]-annulation over the [4 + 21-Diels-Alder alternative. The reaction involves initial nucleophilic addition of the pyrrole moiety at the triple bond followed by tandem ring closure of an anionic intermediate. (C) 2018 Elsevier Ltd. All rights reserved.