Acyclic Diastereoselection in Prochiral Radical Addition to Prochiral Olefins
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- 作者：Mukund P. Sibi ; Tara R. Rheault ; Sithamalli V. Chandramouli ; and Craig P. Jasperse
- 刊名：Journal of the American Chemical Society
- 出版年：2002
- 出版时间：March 27, 2002
- 年：2002
- 卷：124
- 期：12
- 页码：2924 - 2930
- 全文大小：102K
- 年卷期：v.124,no.12(March 27, 2002)
- ISSN：1520-5126
文摘
The stereochemical preference (syn or anti) when prochiral radicals add to prochiral acceptorsis of fundamental interest. The primary focus of this research was to determine which factors influence therelative stereochemistry between the 
and 
chiral centers when these are formed concurrently. Whilemoderate diastereoselectivity was found for addition of alkyl (6a-d) and 
-alkoxy radicals (16a-c) (
6:1syn) to acceptors 4, 7, 8, 10, and 14, consistently high selectivity was observed with less reactive halogenatedradicals (6f,g) (>15:1 anti). Steric influence in alkyl radical additions was difficult to evaluate due to decreasedreactivity when using bulky reaction partners; however, more reactive -alkoxy radicals, it was found thatincreasing steric bulk leads to moderate increases in selectivity. In addition, higher selectivity was observedwhen employing lanthanide Lewis acids whose environment (reactivity) was modified using achiral additives,suggesting a potentially simple means for selectivity enhancements in radical reactions. Overall these resultsindicate that significant stereoelectronic effects are necessary to achieve high levels of selectivity in prochiralradical additions to prochiral acceptors.
and chiral centers when these are formed concurrently. Whilemoderate diastereoselectivity was found for addition of alkyl (6a-d) and -alkoxy radicals (16a-c) (6:1syn) to acceptors 4, 7, 8, 10, and 14, consistently high selectivity was observed with less reactive halogenatedradicals (6f,g) (>15:1 anti). Steric influence in alkyl radical additions was difficult to evaluate due to decreasedreactivity when using bulky reaction partners; however, more reactive -alkoxy radicals, it was found thatincreasing steric bulk leads to moderate increases in selectivity. In addition, higher selectivity was observedwhen employing lanthanide Lewis acids whose environment (reactivity) was modified using achiral additives,suggesting a potentially simple means for selectivity enhancements in radical reactions. Overall these resultsindicate that significant stereoelectronic effects are necessary to achieve high levels of selectivity in prochiralradical additions to prochiral acceptors.