Cyclooctatetraene

1,3,5,7-Cyclooctatetraene (COT) is an unsaturated derivative of cyclooctane. It is a colorless flammable liquid at room temperature. In contrast to benzene-like rings that are planar and have aromaticity, COT has a non-planar 'tub' conformation, which prevents all of the π orbitals from forming a single conjugated system. It is therefore nonaromatic, possessing significant polyene character and undergoing many reactions that benzene rings will not. Cyclooctatetraenide anion, the dianionic derivative of COT, is a aromatic planar structure used as a ligand in organometallic complexes.

History

1,3,5,7-Cyclooctatetraene was initially synthesized by Richard Willstätter in Munich in 1905 using pseudopelletierine as the starting material and the Hofmann elimination as the key transformation:

Willstätter noted that the compound did not exhibit the expected aromaticity. Between 1939 and 1943, chemists throughout the US unsuccessfully attempted to synthesize COT. They rationalized their lack of success with the conclusion that Willstätter had not actually synthesized the compound but instead its isomer, styrene. Willstätter responded to these reviews in his autobiography, where he noted that the American chemists were 'untroubled' by the reduction of his cyclooctatetraene to cyclooctane (a reaction impossible for styrene). During World War II, Walter Reppe at BASF Ludwigshafen developed a simple, one-step synthesis of cyclooctatetraene from acetylene, providing material identical to that prepared by Willstätter. Any remaining doubts on the accuracy of Willstätter's original synthesis were resolved when Arthur C. Cope and co-workers at MIT reported, in 1947, a complete repetition of the Willstätter synthesis, step by step, using the originally reported techniques.