Organocatalytic Dimerization of Ketoketenes

A general method for the catalytic dimerization of ketoketenes is described. Tri-n-butylphosphine was found to be the optimal organocatalyst for the racemic reaction. When lithium iodide was used as an additive, the reaction was rendered selective for dimer formation (dimer/trimer >= 16:1). Ring-opening reactions of the ketoketene dimers as well as preliminary studies toward the development of an asymmetric variant are also reported.