Dibutyl Diels-Alder reaction

Clearly, the effect of the solvent seems to be of great importance to the possibility of MW-specific effects. These could decrease when the polarity of the solvent is increased. This effect was shown in at least two studies by Berlan et al. [19] and, more recently, by Bogdal [34], In the first study acceleration of a nonsymmetric Diels-Alder reaction under the action of MW was much more apparent in xylene than in the more polar dibutyl ether (Fig. 3.4). 

The first report suggesting specific activation of an organic reaction by MW was that of Berlan et al. [28] who observed that some Diels-Alder reactions occurred more rapidly on MW heating than under conventional heating at the same temperature (95 °C). The reactions were performed in two different solvents, xylene and dibutyl ether and the rate enhancements were slightly higher in xylene, the less polar solvent. For example the rate enhancement of the reaction of 2,3-dimethyl-l,3-butadiene 21 with methyl vinyl ketone 22 was 8 times in xylene and 2.3 times in dibutyl ether, based on the half lives of the reactions. Reaction of anthracene 3 with diethyl maleate 23 in xylene (Scheme 4.12) resulted in an approximately fourfold rate in-... 

The Diels-Alder reaction of dibutyl vinylboronate with cyclopentadiene was first reported by Matteson and co-workers in 1963 A mixture of dibutyl endo-norboneneboronate (1) and its exo-isomer (2) in roughly equal amounts was obtained. 

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