Synthesis Of Cis-β-enamine And Thiophene Derivatives By Michael Addition Reaction Of Acetaldehyde

In this article, we have developed some new methods for the synthesis ofcis-β-enaminones and thiophene derivatives through Michael addition ofpropiolaldehydes.The first part, a convenient one-pot strategy for the stereoselective synthesis ofcis-β-enaminones has been developed via the condensation of propiolaldehydes andamines in EtOH. A possible reaction mechanism involved a Michael addition-enoltautomerization-six membered ring transition state is proposed. Under theoptimized conditions, we synthesized20enaminones in high yields (up to97%).The second part, Et3N-catalyzed [3+2] cycloaddition of1,4-dithiane-2,5-diolwith propiolaldehydes has been developed. It involved a tandemMichael-intramolecular Aldol reaction to form the corresponding tetrahydrothiophene.This strategy provides a rapid way to synthesize3-aldehyde-2-substituted thiophenein one portion and the desired products could be obtained in high yields (up to86%),which contain various functional groups.The third part, a formal [3+2] annulation reaction of1,4-dithiane-2,5-diol andN-Substituted Imides through metal-free strategy has been developed. This methodcould furnish2,3-thienoimides in good to high yields (up to86%).