Palladium-Catalyzed Heteroannulation Leading to Heterocyclic Structures with Two Heteroatoms: A Highly Convenient and Facile Method for a Totally Regio- and Stereoselective Synthesis of (<i>Z</i>)-2,3-Dihydro-2-(ylidene)-1,4-benzo- and -naphtho[2,3-<i>b</i>]dioxins
作者:Chinmay Chowdhury、Gopeswar Chaudhuri、Subhadra Guha、Alok k. Mukherjee、Nitya G. Kundu
DOI:10.1021/jo9717595
日期:1998.3.1
A facile method for the synthesis of (Z)-2,3-dihydro-2-(ylidene)-1,4-benzo- and naphthodioxins (3) has been developed using palladium-copper catalysis. Aryl halides 2 were found to react with mono-prop-2-ynylated catechol (1a) or 2-hydroxy-3-(prop-2-ynyloxy)naphthalene (1b) in the presence of (PPh3)(2)PdCl2 (3.5 mol%) and CuI (7 mol%) in triethylamine by stirring at room temperature for 20 h followed by heating at 100 degrees C for 16 h to give products 3 in good yields. The method is regio- and stereoselective and also amenable to bisheteroannulation. The 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 analysis. Based on experimental observations and known palladium chemistry, a mechanism has been proposed to explain the regio- and stereoselective 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-benzodioxinyl functionality at the C-5 position, has been synthesized.