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An enantioselective tandem Michael addition/ cyclization reaction between trisubstituted 2-nitro-1,3-enynes and cyclic 1,3-diketones catalyzed by a chiral organosquaramide catalyst in the presence of Ag2CO3 was developed. The chiral functionalized chromene products could be obtained in good yield and in 80-99% enantiomeric excess. The structures and absolute configurations of some of the products were confirmed by X-ray crystallographic analysis.

Tributylphosphine-catalyzed regioselective [3+2] cycloadditions between ethyl 5,5-diarylpenta2,3,4-trienoate 1 and various aromatic aldehydes 2 to produce a wide variety of polysubstituted 2,5-dihydrofurans 3, and between 1 and beta-unsubstituted alpha,beta-unsaturated carbonyl compounds 5 to give polysubstituted cyclopentenes 6 with a quaternary carbon center, are reported. In both cases the reaction partners approach each other via the sterically less hindered orientation to afford the target products in excellent regioselectivity. The reaction mechanism involved first the generation of a zwitterionic intermediate between the butatriene 1 and PBu3. For the formation of 2,5-dihydrofurans 3, the preferred cyclization mode encompassed the nucleophilic attack of the a-position of butatriene to the aldehydic carbon of 2, followed by the ring closure between the aldehydic oxygen of 2 and the gamma-position of butatriene, which is the first report of a normal [3+2] cycloaddition between cumulenes and aldehydes. For the formation of cyclopentenes 6, the reaction involved attack of the gamma-position of the butatriene to the electron-deficient beta-position of the alpha,beta-unsaturated carbonyl compounds 5, followed by the ring closure between the alpha-position of 5 and the a-position of butatriene, which shows a different regioselectivity to the previously reported [3+2] cycloadditions between butatriene and olefins.