2-COMPLEMENTARY SYNTHESES OF SYMMETRICALLY-TETRASUBSTITUTED CYCLOOCTATETRAENES

Two complementary synthetic approaches to tetrasubstituted cyclooctatetraenes (COT's) have been developed. The first approach involves reaction of terminal acetylenes with AlBr3 and Et3N to generate mixtures of 1,3,5,7- and 1,2,5,6-substituted syn-tricyclo[4.2 .0.02,5]octadienes (TCOD's) in satisfactory yield. These TCOD's can then be thermally or photolytically ring opened to 1,3,5,7- and 1,2,5,6-substituted COT's. Bulky substituents (e.g., tert-butyl, isopropyl) give exclusively 1,3,5,7-substituted TCOD and COT products. In the second approach, 1,3,5,7- (5) and 1,2,5,6-tetrakis-(hydroxymethyl)COT's (6) were generated and isolated in good yield from the Ni(0)-catalyzed tetramerization of propargyl alcohol. These isomers were converted to their corresponding tetrakis-(bromomethyl)COT's 8 and 9. Reduction of 8 and 9 with LiAlH4 afforded 1,3,5,7-tetramethylCOT (10) and 1,2,5,6-tetramethylCOT (11).