Abstract
Treatment of terminal alkenes with Me3SiCHI2, CrCl2, and TMEDA in THF at 25 °C gives cyclopropylsilanes in good to excellent yields.
The trans:cis ratios of the cyclopropylsilanes are improved by replacing Me3SiCHI2 with i-Pr3SiCHBr2 and LiI.
Key words
chromium(II) - cyclopropylsilane - cyclopropane
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The geminal dichromium reagent was generated by stirring Me3SiCHI2 (1.0 mmol) and CrCl2 (4.0 mmol) in THF at 25 °C for 1 h (Scheme
[2]
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[3b]
In contrast, when TMEDA (4.0 mmol) was added to the geminal dichromium reagent generated
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benzyl ether (2.0 mmol) with the base-added reagent at 25 °C for 4 h gave 1a in 70% yield (based on Me3SiCHI2, trans:cis = 68:32) along with unreacted allyl benzyl ether in 63% yield (Scheme
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When the reaction was conducted with allyl benzyl ether (2.0 mmol), Me3SiCHI2 (1.0 mmol), CrCl2 (2.0 mmol), and TMEDA (2.0 mmol), the yield was still 60% based on Me3SiCHI2 (trans:cis = 68:32), and allyl benzyl ether was recovered in 62% yield. The comproportionation
reaction of both 1 equiv of CrX3 and CrX generating 2 equiv of CrX2 could reduce the amount of the required CrCl2.
