Enantioselective nucleophilic addition of Grignard reagents to N-(2-pyridylsulfonyl)imines in the presence of bis(oxazoline) afforded products with good enantioselectivity. Dynamically induced chirality on the sulfur by coordination of a chiral Lewis acid to a pyridyl nitrogen and one of the sulfonyl oxygens fixes the conformation of the complex and induces enantioselectivity. Since the 2-pyridylsulfonyl
Dication C(R1)–N(R2)2 Synthons and their use in the Synthesis of Formamidines, Amidines, and α-Aminonitriles
作者:Lisheng Cai、Ying Han、Sumei Ren、Liangfu Huang
DOI:10.1016/s0040-4020(00)00785-7
日期:2000.10
A combination of amides and 2-pyridinesulfonyl chloride was evaluated as synthons of the dication C(R-1)-N(R-2)(2)(2+). When the substrates were primary amines, high yields of formamidines and amidines were obtained. When the substrates were alpha-aminoamides, alpha-aminonitriles were obtained. Through this process, naturally occurring a-aminoacids can be transformed into chiral alpha-aminonitriles with complete retention of stereochemical configuration. All reactions proceed rapidly at room temperature, and normally finish within 10 min, with yields ranging from 80 to 95% for most cases. Among the sulfonyl chlorides examined, 2-pyridinesulfonyl chloride stands out in both reaction rate and selectivity of formamidine or amidine versus sulfonyl amide. The scope and limitations of the reaction among different types of amides as synthons and amines as substrates were examined. (C) 2000 Elsevier Science Ltd. All rights reserved.