Organocatalysis using protonated 1,2-diamino-1,2-diphenylethane for asymmetric Diels–Alder reaction

Bisammonium salts of mono-N-alkylated chiral 1,2-diamino-1,2-diphenylethane (DPEN) were employed in the catalytic and asymmetric Diels–Alder reaction between cyclopentadiene and crotonaldehyde. The N-3-pentyl diamine·2HCl catalyst shows high endo/exo selectivity and endo-enantioselectivity for the cycloaddition, and this organocatalysis is the first example of the use of a chiral 1,2-diamine to generate an imine intermediate which is activated by an internal ammonium Brønsted acid for the cycloaddition in a wet solvent.