Free Radical-Mediated Intermolecular Conjugate Additions. Effect of the Lewis Acid, Chiral Auxiliary, and Additives on Diastereoselectivity
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- 作者：Mukund P. Sibi ; Jianguo Ji ; Justin B. Sausker ; and Craig P. Jasperse
- 刊名：Journal of the American Chemical Society
- 出版年：1999
- 出版时间：August 25, 1999
- 年：1999
- 卷：121
- 期：33
- 页码：7517 - 7526
- 全文大小：117K
- 年卷期：v.121,no.33(August 25, 1999)
- ISSN：1520-5126
文摘
We have developed a highly diastereoselective method for the conjugate addition of carbon radicalsto chiral 
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-unsaturated N-enoyloxazolidinones using Bu3SnH as chain carrier and Et3B/O2 as radical initiator.Lewis acids have been screened, and Yb(OTf)3 proved to give optimized results for both chemical yield (88%for 1a and 94% for 1b) and diastereoselectivity (25:1 for 1a and 46:1 for 1b). The selectivity is solvent-dependent, CH2Cl2-THF being an ideal combination. Scrupulously dry solvents or reaction conditions werenot required. Substoichiometric amounts of Yb(OTf)3 provided efficient reaction with minimal sacrifice indiastereoselectivity. Carbon radicals with reasonable nucleophilicity were generally successful, includingfunctionalized radicals such as acetyl or methoxymethyl. Electrophilic radicals were not successful. A modelwhich accounts for most of our observations is presented.
,-unsaturated N-enoyloxazolidinones using Bu3SnH as chain carrier and Et3B/O2 as radical initiator.Lewis acids have been screened, and Yb(OTf)3 proved to give optimized results for both chemical yield (88%for 1a and 94% for 1b) and diastereoselectivity (25:1 for 1a and 46:1 for 1b). The selectivity is solvent-dependent, CH2Cl2-THF being an ideal combination. Scrupulously dry solvents or reaction conditions werenot required. Substoichiometric amounts of Yb(OTf)3 provided efficient reaction with minimal sacrifice indiastereoselectivity. Carbon radicals with reasonable nucleophilicity were generally successful, includingfunctionalized radicals such as acetyl or methoxymethyl. Electrophilic radicals were not successful. A modelwhich accounts for most of our observations is presented.