Abstract
AbstractThe preparation of the title compounds 9−11 was achieved by catalytic hydrogenation of 1,8‐diazabicyclo[6.6.6]eicosa‐4,11‐diyne (13), 1,8‐diazabicyclo[6.6.5]nonadeca‐4,11‐diyne (14), and 1,8‐diazabicyclo[6.6.4]octadeca‐4,11‐diyne (15), respectively. As catalyst we used Pd(OH)2 on carbon. NMR studies on 9−11 revealed an in/in conformation at the bridgehead positions. Treatment of 9−11 with an excess of trifluoroacetic acid yielded, in a kinetically controlled reaction, mixtures of the out/out and in/out diprotonated species [9·2H]2+, [10·2H]2+ and [11·2H]2+. The thermodynamically controlled species, the corresponding in/in conformers, are formed at higher temperatures and longer reaction times. The experimental observations are supported by AM1 calculations. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)
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