Synlett 2009(10): 1670-1674  
DOI: 10.1055/s-0029-1217345
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© Georg Thieme Verlag Stuttgart ˙ New York

Acid-Base Dual-Functional Catalysis by Axially Chiral Guanidine in Enantioselective [3+2] Cycloaddition of Maleate to Schiff Bases as a Precursor of Azomethine Ylides

Megumi Nakano, Masahiro Terada*
Department of Chemistry, Graduate School of Science, Tohoku University, Aoba-ku, Sendai 980-8578, Japan
Fax: +81(22)795-6602; e-Mail: mterada@mail.tains.tohoku.ac.jp;
Further Information

Publication History

Received 22 February 2009
Publication Date:
02 June 2009 (online)

Abstract

The enantioselective [3+2] cycloaddition reaction of dimethyl maleate with Schiff bases as the precursor of azomethine ylide was developed using axially chiral guanidine catalysts to provide optically active pyrrolidine derivatives. Acid-base dual-functional catalysis by an axially chiral guanidine through double hydrogen-bonding interaction is proposed to give the cycloaddition products in good yields.

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Compound 4a: white solid. HPLC analysis Chiralpak AD-H (hexane-i-PrOH = 70:30, 1.0 mL/min, 210 nm, 30 ˚C): t R = 16.5 (minor), 39.2 (major) min. ¹H NMR (300 MHz, CDCl3): δ = 1.28 (3 H, t, J = 7.2 Hz), 3.24 (3 H, s), 3.57-3.63 (1 H, m), 3.68 (3 H, s), 3.68-3.74 (1 H, m), 4.13 (1 H, d, J = 8.4 Hz), 4.23 (2 H, q, J = 7.2 Hz), 4.52 (1 H, d, J = 7.2 Hz), 7.49 (2 H, d, J = 8.4 Hz), 7.61 (2 H, d, J = 8.4 Hz). ¹³C NMR (75.5 MHz, CDCl3): δ = 14.0, 50.7, 51.5, 52.1, 61.5, 62.2, 64.6, 111.5, 118.5, 127.6, 132.0, 143.1, 170.2. 170.3, 170.5. ESI-HRMS: m/z calcd for C18H20N2O6 [M + Na]+: 383.1214; found: 383.1213. [α]D ²² -47.1 (c 0.99, CHCl3).

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Compound 4e: white solid. HPLC analysis Chiralpak AS-H (hexane-i-PrOH = 70:30, 1.0 mL/min, 210 nm, 30 ˚C): t R = 8.7 (2S,3R,4R,5R), 23.6 (2R,3S,4S,5S) min. ¹H NMR (300 MHz, CDCl3): δ = 1.29 (3 H, t, J = 7.2 Hz), 3.26 (3 H, s), 3.52-3.57 (1 H, m), 3.65-3.72 (1 H, m), 3.68 (3 H, s), 4.12 (1 H, d, J = 8.4 Hz), 4.22 (2 H, q, J = 7.2 Hz), 4.46 (1 H, d, J = 7.2 Hz), 7.29 (4 H, s). ¹³C NMR (75.5 MHz, CDCl3): δ = 14.1, 50.7, 51.4, 52.0, 52.3, 61.5, 62.3, 64.6, 128.3, 128.4, 133.5, 135.9, 170.4. 170.6, 170.7. ESI-HRMS: m/z calcd for C17H20ClNO6 [M + Na]+: 392.0871; found: 392.0870. [α]D ²² -47.6 (c 1.0, CH2Cl2); lit.¹0h [a]D ²0 62.7 (c 1.0, CH2Cl2, 98% ee).

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The intramolecular reaction of 1,4-addition product 5a using TMG or DBU as organic base catalyst (2 mol%), instead of chiral catalyst (R)-1e, did not provide cyclization product 4a at all under the same reaction conditions.