Free radical-mediated intermolecular conjugate additions. Effect of the Lewis acid, chiral auxiliary, and additives on diastereoselectivity

被引：87

作者：

Sibi, MP ^{[1
]}

Ji, JG ^{[1
]}

Sausker, JB ^{[1
]}

Jasperse, CP ^{[1
]}

机构：

[1] N Dakota State Univ, Dept Chem, Fargo, ND 58105 USA

来源：

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY | 1999年 / 121卷 / 33期

关键词：

D O I：

10.1021/ja991205e

中图分类号：

O6 [化学];

学科分类号：

0703 ;

摘要：

We have developed a highly diastereoselective method for the conjugate addition of carbon radicals to chiral alpha,beta-unsaturated N-enoyloxazolidinones using Bu3SnH as chain carrier and Et3B/O-2 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 were not required. Substoichiometric amounts of Yb(OTf)(3) provided efficient reaction with minimal sacrifice in diastereoselectivity. Carbon radicals with reasonable nucleophilicity were generally successful, including functionalized radicals such as acetyl or methoxymethyl. Electrophilic radicals were not successful. A model which accounts for most of our observations is presented.

引用

页码：7517 / 7526

页数：10

共 67 条

[1] Asymmetric total synthesis of (+)-tolterodine, a new muscarinic receptor antagonist, via copper-assisted asymmetric conjugate addition of aryl Grignard reagents to 3-phenyl-prop-2-enoyl-oxazolidinones [J].