Controlling Asymmetric Remote and Cascade 1,3-Dipolar Cycloaddition Reactions by Organocatalysis.

The regio- and stereoselective control of cycloaddition reactions to polyconjugated systems has been demonstrated by applying asymmetric organocatalysis. Reaction of 2,4-dienals with nitrones allows for a highly regio- and stereoselective 1,3-dipolar cycloaddition in the presence of an aminocatalyst. The first cycloaddition on the remote olefin can be followed either by a cascade reaction or by other selective reactions of the remaining olefin. The chiral products are obtained in good to high yields and excellent diastereo- and enantioselectivities. The remote selective concept has been extended to 2,4,6-trienals by means of a novel enantioselective triple cascade 1,3-dipolar cycloaddition reaction. The formation of chiral poly 1,3-amino alcohols is also demonstrated.

Trienamine-mediated asymmetric [4+2]-cycloaddition of α,ß-unsaturated ester surrogates applying 4-nitro-5-styrylisoxazoles.

Highly enantioselective organocatalytic [4+2]-cycloaddition of in situ generated trienamines with 4-nitro-5-styrylisoxazoles as α,ß-unsaturated ester surrogates is presented. The synthetic utility of this strategy is demonstrated by transforming the formed cycloadducts into optically active carboxylates.