Ultrasound in Baylis-Hillman reactions with aliphatic and aromatic aldehydes: scope and limitations

The utilization of ultrasound radiation in the Baylis-Hillman reaction with several aldehydes (aromatics and aliphatics) and different alpha,beta-unsaturated reactants is described. For all aldehydes tested, the utilization of ultrasound sources augmented the reaction rate and the chemical yields. The use of ultrasound with two different catalysts (tri-n-butylphosphine and 1,4-diazabicyclo[2.2.2] octane [DABCO]) was also investigated. It was clearly demonstrated that DABCO is much more effective for catalyzing a Baylis-Hillman reaction under the influence of ultrasound than is tri-n-butylphosphine. No effect on reaction rate was observed when the concentration of DABCO was increased. (C) 2002 Elsevier Science Ltd. All rights reserved.