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Paper | Regular issue | Vol 81, No. 7, 2010, pp.1669-1688
Published online, 9th June, 2010
DOI: 10.3987/COM-10-11967
■ Asymmetric 1,3-Dipolar Cycloaddition Reactions of Azomethine Imines with Acrolein Catalyzed by L-Proline and Its Derivatives

Hiroyuki Suga,* Tadashi Arikawa, Kennosuke Itoh, Yukihisa Okumura, Akikazu Kakehi, and Motoo Shiro

*Department of Chemistry and Material Engineering, Faculty of Engineering, Shinshu University, 4-17-1 Wakasato, Nagano 380-8553, Japan

Abstract

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 (exo/endo 91:9 ~ 99:1) and enantioselectivities (75 ~ 98% ee). In contrast, reactions catalyzed by L-proline (30 mol%) under similar conditions favored the endo-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.