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-dihydrobenzo[1,4]dioxineand 3-[(dialkylcarbamoyl)methylene]-3,4-dihydro-2H-benzo-[1,4]oxazine derivatives (3 and 5, respectively) were synthesizedfor the first time starting from readily available 2-prop-2-ynyloxyphenols 1 and 2-prop-2-ynyloxyanilines 4, respectively,through tandem oxidative aminocarbonylation of thetriple bondsintramolecular conjugate addition. Reactionswere carried out in the presence of catalytic amounts of PdI2in conjunction with an excess of KI in N,N-dimethylacetamide(DMA) as the solvent at 80-100 °C and under 20 atm(at 25 °C) of a 4:1 mixture of CO-air. The reaction showeda significant degree of stereoselectivity, the Z isomers beingformed preferentially or exclusively. The configurationaround the double bond of the major stereoisomers wasunequivocally established by X-ray diffraction analysis.