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Synlett 2012; 23(19): 2850-2852
DOI: 10.1055/s-0032-1317474
letter
© Georg Thieme Verlag Stuttgart · New York

Efficient One-pot Synthesis of 1H-Pyrazolo[1,5-b]indazoles by a Domino Staudinger–Aza-Wittig Cyclization

Fen-Fen Zhao
a   Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Central China Normal University, Wuhan 430079, P. R. of China
,
Yan-Mei Yan
a   Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Central China Normal University, Wuhan 430079, P. R. of China
,
Rui Zhang
b   College of Chemistry and Molecular Sciences, Wuhan University, Wuhan, 430072, P. R. of China   Fax: +86(27)67862041   Email: mwding@mail.ccnu.edu.cn
,
Ming-Wu Ding*
a   Key Laboratory of Pesticide & Chemical Biology of Ministry of Education, Central China Normal University, Wuhan 430079, P. R. of China
› Author Affiliations
Further Information

Publication History

Received: 25 August 2012

Accepted after revision: 20 September 2012

Publication Date:
18 October 2012 (online)

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Abstract

1H-Pyrazolo[1,5-b]indazoles were prepared via a domino Staudinger–aza-Wittig cyclization in one-pot fashion, starting from easily accessible azides and triphenylphosphine.

Key words

1H-pyrazolo[1,5-b]indazole - domino reaction - aza-Wittig reaction - azide - iminophosphorane

Supporting Information

    for this article is available online at http://www.thieme-connect.com/ejournals/toc/synlett.
  • Supporting Information
 

  • References and Notes

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  • 12 General Procedure for the Preparation of Azides 5 To a mixture of piperidine (0.85 g, 10 mmol) and AcOH (0.6 g, 10 mmol) in EtOH (10 mL) at 0 °C was added 2-azidobenzaldehyde (1.32 g, 10 mmol) and ketone (10 mmol). After stirring for 1–2 h, the solvent was evaporated under vacuum, and the residue was recrystallized to give the azide 5. Compound 5a: light yellow solid (yield 89%), mp 75–76 °C. 1H NMR (600 MHz, CDCl3): δ = 7.80 (s, 1 H, =CH), 7.46–7.11 (m, 4 H, ArH), 4.30–4.25 (m, 2 H, OCH2), 2.45 (s, 3 H, CH3), 1.24–1.20 (m, 3 H, CH3) ppm. 13C NMR (150 MHz, CDCl3): d = 194.7, 167.1, 139.3, 136.2, 135.5, 131.6, 128.9, 124.6, 118.3, 61.5, 26.4, 13.7 ppm. MS (EI, 70 eV): m/z (%) = 259 (4) [M+], 231 (12), 217 (19), 203 (27), 143 (100), 115 (58). Anal. Calcd for C13H13N3O3: C, 60.22; H, 5.05; N, 16.21. Found: C, 60.01; H, 4.92; N, 16.02.
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