PALLADIUM-CATALYZED HETEROANNULATION LEADING TO HETEROCYCLIC STRUCTURES WITH 2 HETEROATOMS - A HIGHLY CONVENIENT AND FACILE METHOD FOR A TOTALLY REGIOSELECTIVE AND STEREOSELECTIVE SYNTHESIS OF Z)-2,3-DIHYDRO-2-(YLIDENE)-1,4-BENZO[2,3-B]DIOXINS AND -2,3-DIHYDRO-2-(YLIDENE)-1,4-NAPHTHO[2,3-B]DIOXINS

A facile method for the synthesis of (Z)-2,3-dihydro-2-(ylidene)-1,4-b enzo- and naphthodioxins (3) has been developed using palladium-copper catalysis. Aryl halides 2 were found to react with mono-prop-2-ynylat ed catechol (1a) or 2-hydroxy-3-(prop-2-ynyloxy)naphthalene (1b) in th e presence of (PPh3)(2)PdCl2 (3.5 mol%) and CuI (7 mol%) in triethylam ine by stirring at room temperature for 20 h followed by heating at 10 0 degrees C for 16 h to give products 3 in good yields. The method is regio- and stereoselective and also amenable to bisheteroannulation. T he Z-stereochemistry of products 3 was established firmly from H-1 NMR , (3)J(CH) values (between vinylic proton and methylenic carbon of the heterocyclic ring), proton NOE measurements, and finally from X-ray a nalysis. Based on experimental observations and known palladium chemis try, a mechanism has been proposed to explain the regio- and stereosel ective product formation. Some of he products 3 were also converted to 1,4-benzodioxan derivatives 6 using hydrogenation procedure. A uracil derivative of possible biological interest, possessing a 1,4-benzodio xinyl functionality at the C-5 position, has been synthesized.