ASYMMETRIC 1,3-DIPOLAR CYCLOADDITION REACTIONS OF AZOMETHINE IMINES WITH ACROLEIN CATALYZED BY L-PROLINE AND ITS DERIVATIVES

摘要

1,3-Dipolar cycloadditions between acrolein and various N,N'-cyclic azomethine imines in the presence of L-proline and its derivatives as organocatalysts were investigated. Reactions that were catalyzed by (S)-indline-2-carboxylic acid (30 mol%) in CHCl3/MeOH 97:3 (v/v) showed high exo-selectivities (exolendo 91:9 ～ 99:1) and enantioselectivities (75 ～ 98% ee). In contrast, reactions catalyzed by L-proline (30 mol%) under similar conditions favored the ndo-cycloadduct (83:27 ～ 99:1) with modest to good enantioselectivities (31 ～ 83% ee). Based on our studies, the diastereoselective mechanism of the L-proline-catalyzed reaction was found to involve the isomerization of the exo- to the endo-cycloadduct in the presence of L-proline.