Two complementary synthetic approaches to tetrasubstituted cyclooctatetraenes (COT's) have been developed.The first approach involves reaction of terminal acetylenes with AIBr3 and E t3N to generate mixtures of 1,3,5,7-and 1,2,5,6-substituted syntricyclo[ 4.2.0.0 2 • 5 ]octadienes (TCOO's) in high yield."These TCOO's can then be thermally or photolytically ring opened to 1,3,5,7-and 1,2,5,6substituted COT's.Bulkysubstituents (e.g.tert-butyl, isopropyl) give exclusively 1,3,5,7-substituted TCOO and COT products.In the second approach, 1,3,5,7-(4) and 1,2,5,6-( 5) tetrakis(hydroxymethyl) COT's are generated and isolated in good yield from the Ni(O)-catalyzed tetramerization of propargyl alcohol.These isomers are converted to their corresponding tetrakis(bromomethyl)COT's 7 and 8. Reduction of 7 and 8 with LiAII4 affords 1,3,5,7-tetramethyl COT (9) and 1,2,5,6tetramethyl COT (10).Tetrasubst COT v2, October 8, 1992
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Boussie et al. (1993) studied this question.