In this paper, a new cycloaddition
between α,β-unsaturated aldehydes and coumalates realized
under dienamine activation has been described. The reaction proceeds
regioselectively with the distal double bond of the dienamine system
acting as electron-rich dienophile. It leads to the formation of biologically
relevant [2.2.2]-bicyclic lactones. Their functionalization potential
has been confirmed in selected, diastereoselective transformations.
A novel organocatalytic reaction cascade between 3-cyano-4-styrylcoumarins
and 2-mercaptoacetophenones is described. It is based on stereocontrolled
functionalization of cyanocoumarins proceeding in a sequence of thia-Michael/aldol/annulation reactions. This highly diastereo-
and enantioselective reaction is realized by employing enantioselective
bifunctional catalysis and exhibits a broad substrate scope and excellent
functional group tolerance. The synthetic application involves the
transformation of the imidoester group, thus opening access to biologically
relevant coumarin and δ-lactone-fused products.
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