Synthesis and structure of cross-conjugated bis-dehydroannulenes with a Y-enediyne motif and different π-topologies

Abstract

A synthesis of cross-conjugated bis-dehydroannulenes with different topologies of the π electrons by Cu^II-mediated oxidative coupling of the corresponding terminal acetylenic precursors is reported. In general, of the two possible modes of cyclization, which would yield either a [13] annulene or an [18] annulene, the precursors yielded exclusively the bis-dehydro [13] annulenes. However, one example of the formation of a bis-dehydro [18] annulene is also reported. The mode of cyclization to form either the [13] annulene or the [18] annulene is explained on the basis of the conformational preference of the core unit bearing the Y-enediyne moieties. The structures of the two types of bis-annulenes have been unequivocally established by means of single-crystal X-ray crystallographic analysis.