Synlett 2007(2): 0321-0323  
DOI: 10.1055/s-2007-968016
LETTER
© Georg Thieme Verlag Stuttgart · New York

A Novel NaI-Promoted Ring Expansion of Cyclopropylidene Alcohols to Dihydropyrans

Weijun Fua, Xian Huang*a,b, Ying Lina
a Department of Chemistry, Zhejiang University (Xixi Campus), Hangzhou 310028, P. R. of China
Fax: +86(571)88807077; e-Mail: huangx@mail.hz.zj.cn;
b State Key Laboratory of Organometallic Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, P. R. of China
Further Information

Publication History

Received 15 October 2006
Publication Date:
24 January 2007 (online)

Abstract

A novel and efficient approach to prepare dihydropyrans via the ring expansion of cyclopropylidene alcohols in the presence of NaI in AcOH-MeCN was reported. The key feature in the transformation is the effect of the iodide anion.

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Typical Procedure for the Synthesis of Compound 3.
A solution of 1a (160 mg, 1.0 mmol) with NaI (225 mg, 1.5 mmol) in 5 mL of MeCN-AcOH (10:1) was stirred at 80 °C for 12 h. The mixture was then diluted with 10 mL of H2O and extracted three times with Et2O. The organic phases were combined and dried over MgSO4. After evaporation, the residues were purified via chromatography on silica gel with n-hexane-EtOAc as the eluent to afford 108 mg (67%) of 3a as a liquid. IR (neat): 1652, 1600, 1448 cm-1. 1H NMR (400 MHz, CDCl3): δ = 7.25-7.34 (m, 5 H), 6.19-6.21 (m, 1 H), 4.50 (q, J = 2.8 Hz, 2 H), 3.85 (t, J = 5.6 Hz, 2 H), 2.30-2.34 (m, 2 H). 13C NMR (100 MHz, CDCl3): δ = 138.4, 136.1, 128.5, 127.3, 124.7, 121.2, 66.8, 64.0, 25.5. MS (70 eV): m/z (%) = 160 (36.26) [M+].