Asymmetric Dearomative (3+2)-Cycloaddition Involving Nitro-Substituted Benzoheteroarenes under H-Bonding Catalysis.

In our studies, the organocatalytic 1,3-dipolar cycloaddition between 2-nitrobenzofurans or 2-nitrobenzothiophene and N-2,2,2-trifluoroethyl-substituted isatin imines has been developed. The reaction has been realized by employing bifunctional organocatalysis, with the use of squaramide derivative being crucial for the stereochemical efficiency of the process. The usefulness of the cycloadducts obtained has been confirmed in selected transformations, including aromative and non-aromative removal of the nitro group.

Asymmetric Synthesis of [2.2.2]-Bicyclic Lactones via All-Carbon Inverse-Electron-Demand Diels-Alder Reaction.

In this paper, a new cycloaddition between α,ß-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.

Organocatalytic Synthesis of cis-2,3-Aziridine Aldehydes by a Postreaction Isomerization.

An unprecedented organocatalytic cis-selective aziridination of α,ß-unsaturated aldehydes is described. The strategy utilizes postreaction isomerization as a key step. Our study demonstrates that by a proper choice of structural features of reagents and the catalyst the outcome of well-established reactions can be altered, leading to the formation of normally inaccessible diastereomers. The usefulness of the developed approach has been confirmed in the syn-selective formal aminohydroxylation of α,ß-unsaturated aldehydes.