REGIOSPECIFIC DISPLACEMENT OF THE C-B BOND OF TRIS[4-(SUBSTITUTED)FURAN-3-YL]BOROXINES WITH C-SN BOND AND C-O BOND - SYNTHESES OF 3,4-DISUBSTITUTED FURANS AND 4-SUBSTITUTED-3(2H)-FURANONES

摘要

Tris [4-(substituted)furan-3-yl]boroxines 2, prepared from the corresponding 4-(substituted)-3-(trimethylsilyl)furan 1, were converted successfully to 4-(substituted)-3-(tributylstannyl)furan 3 through palladium-catalyzed cross-coupling reactions with tributylstannyl chloride. Palladium-catalyzed cross-coupling reactions of 3 with organohalides afforded 3,4-disubstituted furans 4. Regiospecific iodination of 4-(trimethylsilyl)-3-(tributylstannyl) furan (3a) gave 4-iodo-3-(trimethylsilyl)furan (5), which reacted with excess ethyl acrylate under a common Heck-condition to produce 2,3-bis(trans-ethoxycarbonylvinyl)-4-(trimethylsilyl)furan (6). A thermal 6 pi-electrocyclic reaction followed by dehydration converted 6 into benzo[2,3-b]furan 8. Oxidation of 2 generated the corresponding 4-substituted-3(2H)-furanones 9. [References: 34]