Ring Expansion to 1‐Bromo‐1‐alumacyclonona‐2,4,6,8‐tetraene by Insertion of Two Alkyne Molecules into the AlC Bonds

Abstract

Treatment of 1-bromo-2,3,4,5-tetraethylalumole (1) with 3-hexyne afforded the corresponding product 1-bromo-1alumacyclonona-2,4,6,8-tetraene (2), accompanied by the formation of hexaethylbenzene.I nt he crystalline state, 2 forms aB r-bridged dimer with ap seudo C 2 -symmetric and twisted AlC 8 nine-membered ring. Deuterium-labeling experiments and DFT calculations on the reaction of 1 with 3-hexyne suggested that 1-bromo-1-alumacyclohepta-2,4,6-triene,which is formed by the insertion of one molecule of 1-hexyne into the AlÀCb ond of alumole 1,i st he key intermediate for the generation of 2 as well as hexaethylbenzene.