SYNTHESIS OF 2,8-DIARYLPYRANO[3,2-G]CHROMENE-4,6-DIONES

3-(3,4,5-trimethoxyphenyl)isoxazol-5-yl]resorcinol 3 was generated in a Stille coupling between 4,6-diiodoresorcinol and 2 mol ributylstanny l-3-(3,4,5-trimethoxyphenyl)isoxazole 2. 4-Iodoresorcinol was coupled with 3-phenyl-5-tributylstannylisoxazole to give 5-(2,4-dihydroxypheny l)-3-phenylisoxazole 7. Selective iodination of 7 with ICl gave 5-(2,4 -dihydroxy-5-iodophenyl)-3-phenyl-isoxazole 8, which underwent Stille coupling with 2 to give 3-(3,4.5-trimethoxyphenyl)isoxazol-5-yl]resorc inol 9. Reductive ring cleavage of 3 and 9 followed by acid-catalysed cyclisation gave 5-trimethoxyphenyl)pyrano[3,2-g]chromene-4,6-dione 4 and 5-trimethoxyphenyl)pyrano[3,2-g]chromene-4,6-dione 10, respectivel y, in fair overall yields.