Ring Expansion to 1‐Bromo‐1‐alumacyclonona‐2,4,6,8‐tetraene by Insertion of Two Alkyne Molecules into the AlC Bonds†
This work was partially supported by the JSPS KAKENHI (Nos. 24109013, 24550048, 2662028, and 15H05477), the MEXT Project of Integrated Research on Chemical Synthesis from the Ministry of Education, Culture, Sports, Science, and Technology (Japan), the “Molecular Systems Research” project of the RIKEN Advanced Science Institute, and the Collaborative Research Program of the Institute for Chemical Research, Kyoto University. T.A. is thankful for the Ube Industries Award in Synthetic Organic Chemistry (Japan).
Abstract
Treatment of 1‐bromo‐2,3,4,5‐tetraethylalumole (1) with 3‐hexyne afforded the corresponding product 1‐bromo‐1‐alumacyclonona‐2,4,6,8‐tetraene (2), accompanied by the formation of hexaethylbenzene. In the crystalline state, 2 forms a Br‐bridged dimer with a pseudo C2‐symmetric and twisted AlC8 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 AlC bond of alumole 1, is the key intermediate for the generation of 2 as well as hexaethylbenzene.
