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Synlett 2015; 26(15): 2170-2174
DOI: 10.1055/s-0034-1381057
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© Georg Thieme Verlag Stuttgart · New York

Y(OTf)3-Catalyzed Cascade Propargylic Substitution/Aza-Meyer–Schuster Rearrangement: Stereoselective Synthesis of α,β-Unsaturated Hydrazones and Their Conversion into Pyrazoles

Wenfei Liu
Inner Mongolia Key Laboratory of Fine Organic Synthesis, Department of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, P. R. of China   eMail: shufengchen@imu.edu.cn   eMail: baoguol@sohu.com
,
Han Wang
Inner Mongolia Key Laboratory of Fine Organic Synthesis, Department of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, P. R. of China   eMail: shufengchen@imu.edu.cn   eMail: baoguol@sohu.com
,
Haiying Zhao
Inner Mongolia Key Laboratory of Fine Organic Synthesis, Department of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, P. R. of China   eMail: shufengchen@imu.edu.cn   eMail: baoguol@sohu.com
,
Baoguo Li*
Inner Mongolia Key Laboratory of Fine Organic Synthesis, Department of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, P. R. of China   eMail: shufengchen@imu.edu.cn   eMail: baoguol@sohu.com
,
Shufeng Chen*
Inner Mongolia Key Laboratory of Fine Organic Synthesis, Department of Chemistry and Chemical Engineering, Inner Mongolia University, Hohhot 010021, P. R. of China   eMail: shufengchen@imu.edu.cn   eMail: baoguol@sohu.com
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Publikationsverlauf

Received: 16. Mai 2015

Accepted after revision: 03. Juli 2015

Publikationsdatum:
12. August 2015 (online)

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Abstract

A straightforward and concise method for the highly stereoselective synthesis of α,β-unsaturated hydrazones by the Y(OTf)3-catalyzed cascade propargylic substitution/aza-Meyer–Schuster rearrangement reaction of tertiary propargylic alcohols and p-toluenesulfonyl hydrazide under an air atmosphere is developed. A series of α,β-unsaturated hydrazones have been synthesized from simple and readily available starting materials in good yields. Furthermore, the obtained α,β-unsaturated hydrazones are converted into pyrazoles in the presence of LiOt-Bu.

Keywords

propargylic alcohols - aza-Meyer–Schuster rearrangement - Y(OTf)3 - α,β-unsaturated hydrazones - pyrazoles

Supporting Information

    Supporting information for this article is available online at http://dx.doi.org/10.1055/s-0034-1381057.
  • Supporting Information
 

  • References and Notes

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  • 8 For the crystal structure of 3a, please see the Supporting Information.
  • 9 General Procedure for the Y(OTf)3-Catalyzed Reaction of Tertiary Propargylic Alcohols with p-Toluenesulfonyl Hydrazide To a solution of propargylic alcohols (0.3 mmol) and p-toluenesulfonyl hydrazide (0.6 mmol) in MeCN (2.0 mL) was added Y(OTf)3 (0.06 mmol) under an air atmosphere. The resulting mixture was heated at 80 °C for the indicated time. After completion of the reaction, the mixture was cooled to r.t. The solvent was removed in a vacuum, and the resulting residue was purified on a silica gel column (PE–EtOAc) to provide the desired α,β-unsaturated hydrazone products 3. Representative Spectroscopic Data Compound 3b: white solid; mp 128–130 °C. 1H NMR (500 MHz, CDCl3): δ = 1.86 (s, 3 H), 2.43 (s, 3 H), 6.19 (s, 1 H), 7.00–7.07 (m, 2 H), 7.33 (d, J = 8.0 Hz, 2 H), 7.39–7.44 (m, 3 H), 7.53–7.55 (m, 2 H), 7.63–7.68 (m, 2 H), 7.84 (s, 1 H), 7.89 (d, J = 8.5 Hz, 2 H). 13C NMR (125 MHz, CDCl3): δ = 18.2, 21.6, 115.5, 125.9, 128.0, 128.8, 128.8, 129.1, 129.7, 131.9, 135.6, 139.5, 144.2, 146.6, 150.9, 162.9, 164.8. ESI-HRMS: m/z calcd for C23H22FN2O2S [M + H]+: 409.1381; found: 409.1379. Compound 3q: white solid; mp 114–117 °C. 1H NMR (500 MHz, CDCl3): δ = 1.29 (s, 6 H), 2.43 (s, 3 H), 3.65 (s, 1 H), 6.07 (s, 1 H), 7.30 (d, J = 7.0 Hz, 5 H), 7.36–7.39 (m, 2 H), 7.83(d, J = 8.0 Hz, 2 H). 13C NMR (125 MHz, CDCl3): δ = 21.6, 27.0, 83.3, 91.6, 122.4, 128.3, 128.3, 128.4, 129.4, 131.7, 135.3, 143.8. Anal. Calcd for C18H20N2O2S: C, 65.83; H, 6.14; N, 8.53. Found: C, 65.81; H, 6.20; N, 8.41.
  • 12 General Procedure for the Synthesis of Pyrazoles from the Corresponding α,β-Unsaturated Hydrazones To a solution of α,β-unsaturated hydrazones (0.3 mmol) in toluene (2.0 mL) was added LiOt-Bu (0.45 mmol) under an air atmosphere. The resulting mixture was heated at 80 °C for the indicated time. After completion of the reaction, the solvent was removed in a vacuum. The resulting residue was purified on a silica gel column (EtOAc–PE) to provide the desired pyrazole products 4 and 5. Representative Spectroscopic DataCompound 4a: yellow solid; mp 68–71 °C. 1H NMR (500 MHz, CDCl3): δ = 1.83 (s, 3 H), 7.28–7.36 (m, 4 H), 7.39–7.44 (m, 3 H), 7.48 (t, J = 7.5 Hz, 2 H), 8.12–8.05 (m, 2 H). 13C NMR (125 MHz, CDCl3): δ = 22.2, 100.3, 126.5, 127.3, 128.1, 128.8, 128.9, 129.3, 130.7, 136.34, 136.6, 154.9. ESI-HRMS: m/z calcd for C16H15N2 [M + H]+: 235.1230; found: 235.1230. Compound 4f: yellow solid; mp 84–87 °C. 1H NMR (500 MHz, CDCl3): δ = 1.80 (s, 3 H), 7.29 (d, J = 8.5 Hz, 2 H), 7.41–7.51 (m, 5 H), 8.07 (d, J = 8.0 Hz, 2 H). 13C NMR (125 MHz, CDCl3): δ = 22.2, 99.7, 122.1, 127.3, 128.2, 129.0, 129.5, 130.4, 131.9, 135.4, 135.8, 155.3. Anal. Calcd for C16H13BrN2: C, 61.36; H, 4.18; N, 8.94. Found: C, 61.29; H, 4.31; N, 8.95.