[4+2] cycloadditions of nitroalkenes in water. Highly asymmetric synthesisof functionalized nitronates

The [4 + 2] cycloadditions of (E)-2-aryl-1-cyano-1-nitroalkenes 1 with achi ral and enantiopure vinyl ethers 2 and 3 carried out in sole water are repo rted. These reactions occur in a heterogeneous phase under mild conditions and are fast and highly stereoselective. By using(-)-N,N-dicyclohexyl-(1S)- isoborneol-10-sulfonamide as achiral auxiliary, the cycloadditions are tota lly asymmetric. The face selectivity is discussed in terms of the shape of the chiral auxiliary and the reactive conformation of vinyl ether.