Tin Tetrachloride‐Catalyzed Regiospecific Allylic Substitution of Quinone Monoketals: An Easy Entry to Benzofurans and Coumestans

Ying Liu; Jingxin Liu; Mang Wang; Jun Liu; Qun Liu

doi:10.1002/adsc.201200344

journal article Sep 28, 2012

Tin Tetrachloride‐Catalyzed Regiospecific Allylic Substitution of Quinone Monoketals: An Easy Entry to Benzofurans and Coumestans

Ying Liu

Jingxin Liu

Mang Wang Jun Liu

Qun Liu

Advanced Synthesis & Catalysis Vol. 354 No. 14-15 pp. 2678-2682 · Wiley

View at Publisher Save 10.1002/adsc.201200344

Abstract

AbstractA highly regioselective allylic substitution of quinone monoketals with α‐oxoketene dithioacetals is achieved under the catalysis of only tin tetrachloride (1 mol%). The advantages of the reaction, including its simplicity, rapidity, low catalyst loading of inexpensive tin tetrachloride, mild conditions and; in particular, the regiospecificity, is proposed to be due to a pseudo‐intramolecular process. This new synthetic method provides a facile [3+2] cycloaddition route to benzofurans and is highlighted by the synthesis of coumestans.

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Aiming to synthesize coumestan4(also see Scheme 2) we also designed the following process. But it failed.

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13C NMR (125 MHz CDCl3) for1a:δ=185.0 143.2 (2 C) 129.9 (2 C) 92.4 50.3 (2 C). The13C NMR analysis of1ain the presence of 0.1 equiv. of SnCl4was performed as follows: to a solution of1a(39 mg) in 0.5 mL of CDCl3was added SnCl4(0.29 ul 0.1 equiv.). Then 13C NMR spectra of the resulting solution were recorded at 25 °C on a Varian 125 MHz. It was found that the13C NMR spectra of1ain the presence of 0.1 equiv. of SnCl4were complex. The peaks ofδCO andδC(OMe)2of1aturned out to be weak and some new peaks such as those at 187.2 ppm 157.3 ppm 136 5 ppm 99.6 ppm and 55.5 ppm were observed. These results show clearly the interactions of both the carbonyl oxygen and methoxy oxygen of1awith SnCl4and supported the formation of intermediateA.

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A comparative reaction between1aand vinyl sulfide was carried out under identical conditions. However no reaction was detected with 1 mol% of SnCl4. In the presence of 3 mol% of SnCl4 the reaction gave cycloaddition product 5‐methoxy‐2‐(phenylthio)‐2 3‐dihydrobenzofuran in 42% yield in 30 min. In addition we also prepared [2‐(4‐chlorophenyl)ethene‐1 1‐diyl]bis(methyl sulfane) to react with1aunder the catalysis of 1 mol% of SnCl4in MeCN at room temperature. However no reaction was detected after 3 h at room temperature.

Metrics

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Citations

48

References

Details

Published: Sep 28, 2012
Vol/Issue: 354(14-15)
Pages: 2678-2682
License: View

Authors

Y

Ying Liu

Harbin Institute of Technology

University of Michigan

Q

Qun Liu

Cite This Article

Ying Liu, Jingxin Liu, Mang Wang, et al. (2012). Tin Tetrachloride‐Catalyzed Regiospecific Allylic Substitution of Quinone Monoketals: An Easy Entry to Benzofurans and Coumestans. Advanced Synthesis & Catalysis, 354(14-15), 2678-2682. https://doi.org/10.1002/adsc.201200344

Tin Tetrachloride‐Catalyzed Regiospecific Allylic Substitution of Quinone Monoketals: An Easy Entry to Benzofurans and Coumestans

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