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DOI: 10.1055/s-2004-825612
Preparation of Cyclopropylsilanes from Terminal Alkenes with Organochromium Reagents
Publication History
Publication Date:
18 May 2004 (online)
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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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6a Oxidation of 5 with pyridinium chlorochromate produced the corresponding ketone in 83% yield, which was identical to the ketone in the following literature:
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6b
The structure of 5 was also confirmed by X-ray crystallography.
- 7 A chromium-alkylidene complex having a TMEDA ligand was isolated, see:
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References
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] ). Treatment of 3-phenylpropanal (2.0 mmol) with the reagent gave trimethyl(4-phenyl-1-butenyl)silane in 75% yield (E:Z = >99:<1) after stirring at 25 °C for 4 h; the aldehyde was recovered in 47% yield. [3b] In contrast, when TMEDA (4.0 mmol) was added to the geminal dichromium reagent generated at 25 °C for 1 h and the mixture was stirred for a further 15 min, treatment of allyl 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 [2] ). These results suggest that the reactive species of the silylcyclopropanation is not a carbenoid but the species derived from 6 and TMEDA.
11When 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.