A strain induced change of mechanism from a [2 + 2 + 2] to a [2 + 1 + 2 + 1] cycloaddition reaction.
While investigating the [2 + 2 + 2] cycloaddition as a tool to build up strained oligophenyl systems with a diyne-ethylene glycol macrocyle, a surprising change of mechanism was observed. Instead of the expected [2 + 2 + 2] para-terphenyl, the ortho-terphenyl product explained by a formal [2 + 1 + 2 + 1] cycloaddition was formed. An η(4)-coordinated metal-cyclobutadiene is proposed as the key structure in the catalytic cycle, which is formed to release the induced strain. The optical properties of the ortho-terphenyl products have been measured as well as the coordination ability of Na(+) and K(+).
Department of Chemistry, Basel University , St Johanns-Ring 19, CH-4056 Basel, Switzerland.
Anne-Florence
AF
Tran-Van
Silas
S
Götz
Markus
M
Neuburger
Hermann A
HA
Wegner