Chiral Diamine-Salts for Catalytic exo-selective Diels-Alder Reactions

Significance

A highly exo-selective and enantio­selective organocatalytic Diels-Alder (DA) reaction has been developed. Various α,β-unsaturated alde­hydes 2 undergo DA reaction with cyclopentadiene (3) when N-methylaniline derivatives and protonic acids are used as catalysts. N-methylaniline-TsOH itself gave exo-4 (R = Ph) in 75% yield and 2.2:1 selectivity. Exceedingly high exo-selectivities (from 6:1 to >20:1) could be obtained when catalyst 1 together with p-toluenesulfonic acid or related chiral diamine salts at -20 °C with α,α,α-trifluoro­toluene as solvent were used. Moderate to high enantioselectivities (27-92%) have been obtained. The use of salts derived from primary amines did not yield any products.