Asymmetric oxa-Diels-Alder reactions using carbonyl compounds as dienes or dienophiles are effective tool for synthesis of various chiral pyran derivatives. [1, 2]  The first asymmetric oxa-Diels-Alder reaction of a,β-unsaturated ketones, which were activated through dienamines, with aldehydes described Xiao [3]. The best yields were achieved with pyrrolidine, but with chiral catalysts the yields dramatically dropped and the best ee was only 40 %.

With regards to the fact, that oxa-Diels-Alder reactions of a,β-unsaturated ketones as precursors of dienes with aldehydes have been described just once untill now [3] and suffer from long reaction time and/or mediocre yields and selectivities, we decided to study reaction of (E)-4-phenylbut-3-en-2-one with 4-nitrobenzaldehyde under various, classical as well as non-classical (ultrasonic or microwave irradiation, ball milling, continuous flow microreactor) conditions. We have tested a range of chiral organocatalysts. As a selection principle we have chosen catalyst ability to participate in an enamine activation of a,β-unsaturated ketone as well ability to hydrogen bond activation.