Experimental Results and Computational Insight into Sequential Reactions of beta-(2-aminophenyl)-alpha,beta-Ynones with Aryl Isocyanates/Benzoyl Isothiocyanate

The investigation on tandem addition/cyclization reactions of -(2-aminophenyl) ,-ynones with aryl isocyanates/ benzoyl isothiocyanate is reported. Experimental results show the suitable conditions to selectivity direct the reaction outcome towards the product of 6-exo-dig N-, O-, or S-annulation of the in situ generated alkynyl urea/thiourea intermediate. The reaction of a variety of β-(2-aminophenyl) α,β-ynones with aryl isocyanates/ benzoyl isothiocyanate afforded the selective formation of quinazoline or benzoxazine / benzothiazine derivatives, respectively. Density Functional Theory calculations provide a plausible rationale for the reaction outcome.