Benzannulenones. Synthesis of 22,23,24,25-tetradehydrodibenzo[a,g]cycloheneicosen-11-one

Abstract

The conjugated ω-(o-ethynylphenyl)alka-dienal (6) and -trienal (7) were prepared and converted by aldol condensations into acyclic ketones, required as potential precursors of tetradehydrodibenzannulenones. Only the bis(ethynylphenyl)tridecahexaenone (1d) afforded the corresponding annulenone, 22,23,24,25-tetradehydrodibenzo[a,g]cycloheneicosen-11-one (2d). The ¹H n.m.r. spectrum showed that (2d) is an atropic molecule.