Diels-Alder reactions of 2-oxazolidinone dienes in polar solvents using catalysis or non-conventional energy sources

The(Z)-N-substituted 4-methylene-5-propylidene-2-oxazolidinone dienes were prepared by a one-step synthesis, starting from 2,3-hexanedione and isocyanates. Diels-Alder cycloadditions of these dienes were carried out in the presence of the dienophiles methyl vinyl ketone, methyl propiolate, and a captodative olefin, under conditions such as solvents of high polarity, Lewis acid catalysis, and non-conventional energy sources. The reactions carried out either with mixtures of H2O/MeOH or under BF3 . Et2O catalysis yielded the highest regio- and stereoselectivities. The use of ionic liquids, microwaves, and ultrasound did not significantly increase the selectivity.