(S)-Pyrrolidin-2-ylmethyl-1,2,3-triazolium Salts - Ionic Liquid Supported Organocatalysts for Enantioselective Michael Additions to β-Nitrostyrenes

Abstract

(S)-Pyrrolidin-2-ylmethyl-1,2,3-triazolium salts were synthesized as new task-specific ionic liquids via click reaction and alkylation. They serve as excellent recyclable catalysts in enantioselective Michael additions to nitrostyrenes in excess of carbonyl compounds as reactant and as solvent providing high yields and stereoselectivities.

Key words

asymmetric organocatalysis - ionic liquids - Michael addition - task-specific ionic liquids

References and Notes

• 1 Berner OM. Tedeschi L. Enders D. Eur. J. Org. Chem.  2002,  1877 
• 2 Palomo C. Vera S. Mielgo A. Gomez-Bengoa E. Angew. Chem. Int. Ed.  2006,  45:  5984 
• 3 Zhu S. Yu S. Ma D. Angew. Chem.  2008,  120:  555 
• 4 Wu LY. Yan ZY. Xie YX. Niu YN. Liang YM. Tetrahedron: Asymmetry  2007,  18:  2086 
• 5 Herrera RP. Sgarzani V. Bernardi L. Ricci A. Angew. Chem. Int. Ed.  2005,  44:  6576 
• 6 Menozzi C. Dalko PI. In Enantioselective Organocatalysis   Dalko PI. Wiley-VCH; Weinheim: 2007.  p.151 
• 7 Ishii T. Fujioka S. Sekiguchi Y. Kotsuki H. J. Am. Chem. Soc.  2004,  126:  9558 
• 8 Mase N. Thayumanavan R. Tanaka F. Barbas CF. Org. Lett.  2004,  6:  2527 
• 9 Betancort JM. Sakthivel K. Thayumanavan R. Tanaka F. Barbas CF. Synthesis  2004,  1509 
• 10 Alexakis A. Andrey O. Org. Lett.  2002,  4:  3611 
• 11 Mosse S. Andrey O. Alexakis A. Chimia  2006,  60:  216 
• 12 Andrey O. Alexakis A. Tomassini A. Bernardinelli G. Adv. Synth. Catal.  2004,  346:  1147 
• 13 Andrey O. Vidonne A. Alexakis A. Tetrahedron Lett.  2003,  44:  7901 
• 14 Cobb AJA. Shaw DM. Longbottom DA. Gold JB. Ley SV. Org. Biomol. Chem.  2005,  3:  84 
• 15 Cobb AJA. Longbottom DA. Shaw DM. Ley SV. Chem. Commun.  2004,  1808 
• 16 Cao CL. Ye MC. Sun XL. Tang Y. Org. Lett.  2006,  8:  2901 
• 17 Wang W. Wang J. Li H. Angew. Chem. Int. Ed.  2005,  44:  1369 
• 18 Ni B. Zhang Q. Headley AD. Tetrahedron: Asymmetry  2007,  18:  1443 
• 19 Mase N. Watanabe K. Yoda H. Takabe K. Tanaka F. Barbas CF. J. Am. Chem. Soc.  2006,  128:  4966 
• 20 Wiesner M. Revell JD. Wennemers H. Angew. Chem. Int. Ed.  2008,  47:  1871 
• 21 Luo SZ. Mi XL. Liu S. Xu H. Cheng JP. Chem. Commun.  2006,  3687 
• 22 Yan ZY. Niu YN. Wei HL. Wu LY. Zhao YB. Liang YM. Tetrahedron: Asymmetry  2006,  17:  3288 
• 23 Luo SZ. Xu H. Mi XL. Li JY. Zheng XX. Cheng JP. J. Org. Chem.  2006,  71:  9244 
• 24 Hagiwara H. Okabe T. Hoshi T. Suzuki T. J. Mol. Catal. A: Chem.  2004,  214:  167 
• 25 Xu DQ. Luo SP. Yue HD. Wang LP. Liu YK. Xu ZY. Synlett  2006,  2569 
• 26 Ni BK. Zhang QY. Headley AD. Green Chem.  2007,  9:  737 
• 27 Luo SZ. Mi XL. Zhang L. Liu S. Xu H. Cheng JP. Angew. Chem. Int. Ed.  2006,  45:  3093 
• 28 Ni BK. Zhang QY. Headley AD. Tetrahedron Lett.  2008,  49:  1249 
• 29 Hanelt S. Liebscher J. Synlett  2008,  1058 

30

Typical Procedure of Michael Addition of Cyclo-hexanone to Nitrostyrene Nitrostyrene (37 mg, 0.25 mmol) and 4 (10 mol%) were mixed with cyclohexanone (0.5 mL, 5 mmol) in the presence of TFA (0.00625 mmol, 0.2 µL) at r.t. (bulk solution of TFA in cyclohexanone was freshly prepared from 5 µL TFA in 12.5 mL of cyclohexanone). After stirring for 24 h, the homogeneous reaction mixture was diluted with Et₂O to precipitate the catalyst. The organic layer was separated and loaded onto a silica gel column to afford the Michael adduct (60 mg, 98%) as white solid; syn/anti = 99:1, 99% ee [by HPLC on a Chiralpak AD column, λ = 215 nm, eluent
i-PrOH-hexane (10:90), flow rate = 0.8 mL min^-¹; t _R = 10.90 (minor), 15.53 min (major)]. All the Michael addition products are known compounds.