A new synthesis of 2,3-dihydrobenzo[1,4]dioxine and 3,4-dihydro-2H-benzo[1,4]oxazine derivatives by tandem palladium-catalyzed oxidative aminocarbonylation-cyclization of 2-prop-2-ynyloxyphenols and 2-prop-2-ynyloxyanilines

2-(Dialkylcarbamoyl)methylene]-2,3-dihydrobenzo1,4]dioxine and 3-(dialkylcarbamoyl)methylene]-3,4-dihydro-2H-benzo1,4]oxazine derivatives (3 and 5, respectively) were synthesized for the first time starting from readily available 2-prop-2-ynyloxyphenols 1 and 2-prop-2-ynyloxyanilines 4, respectively, through tandem oxidative aminocarbonylation of the triple bond-intramolecular conjugate addition. Reactions were carried out in the presence of catalytic amounts of PdI2 in conjunction with an excess of KI in N,N-dimethylacetamide (DMA) as the solvent at 80-100 degrees C and under 20 atm (at 25 degrees C) of a 4:1 mixture of CO-air. The reaction showed a significant degree of stereoselectivity, the Z isomers being formed preferentially or exclusively. The configuration around the double bond of the major stereoisomers was unequivocally established by X-ray diffraction analysis.