Two 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 AlBr[sub 3] and Et[sub 3]N to generate mixtures of 1,3,5,7- and 1,2,5,6-substituted syn-tricyclo[4.2.0.0[sup 2,5]] 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(O)-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 LiAlH[sub 4] afforded 1,3,5,7-tetramethylCOT (10) and 1,2,5,6-tetramethylCOT (11). 13 refs.