AN IMPROVED SYNTHESIS OF CYCLIC DIALKYNES

An improved synthesis of 1,7-cyclododecadiyne 17 (35 %), 1,7-cyclotrid ecadiyne 18 (65 %), 1,8-cyclotetradecadiyne 19 (85 %), 1,8-cyclopentad ecadiyne 20 (65 %), 1,9-cyclohexadecadiyne 21 (55 %), 1,10-cyclooctade cadiyne 22 (48 %) and 1,12-cyclodocosadiyne 23 (27 %) is reported. Thi s is achieved by treating the dilithium salts of diterminal dialkynes with alpha,omega-dihalogenides. As side products, tetraynes are isolat ed in yields of 1 - 5 %. Furthermore, the synthesis of 6-isopropyliden ethiacyclodeca-3,8-diyne (24) and [10]orthocyclophane-2,8-diyne 29 is reported. The reaction of 24 with CpCo(CO)2 yields a [2.2](2,5)thiophe nophane derivative 30 while 29 gives an intramolecular cyclobutadiene complex 31.