Abstract
Detailed investigations concerning the organocatalytic (asymmetric) α-azidation of prochiral β-ketoesters were carried out. It was shown that the racemic version of such a reaction can either be carried out under oxidative conditions using TMSN3 as the azide-source with quaternary ammonium iodides as the catalysts, or by using hypervalent iodine-based electrophilic azide-transfer reagents with different organocatalysts. In addition, the latter strategy could also be carried out with modest enantioselectivities when using simple cinchona alkaloid catalysts, albeit with relatively low yields.
Highlights
Organic azides are an important and versatile class of molecules, and their syntheses and applications have attracted considerable interest [1,2,3,4,5,6,7,8,9,10]
The use of hypervalent iodine reagents for the transfer of different “uncommon” electrophiles has emerged as a powerful method over the last few years [16,17] and the use of reagents 1 and 2 to facilitate the α-azidation of prochiral nucleophiles represents an impressive application of such reagents
Based on our research focus on asymmetric α-heterofunctionalization reactions [25,26,27,28], as well as our interest in the use of hypervalent iodine reagents under organocatalytic conditions [24], we have, carried out detailed investigations of the α-azidation of ketoesters 3 with the electrophilic azide-transfer reagents 1 and 2 using the chiral organocatalysts C1–C7 shown in Scheme 1 [26,29,30,31,32]
Summary
Organic azides are an important and versatile class of molecules, and their syntheses and applications have attracted considerable interest [1,2,3,4,5,6,7,8,9,10]. Based on our research focus on asymmetric α-heterofunctionalization reactions [25,26,27,28], as well as our interest in the use of hypervalent iodine reagents under organocatalytic conditions [24], we have, carried out detailed investigations of the α-azidation of ketoesters 3 with the electrophilic azide-transfer reagents 1 and 2 using the chiral organocatalysts C1–C7 shown in Scheme 1 [26,29,30,31,32]. Targeted α-azidation of β-ketoesters 3 using TMSN3 under oxidative conditions using the chiral ammonium iodide catalyst C1
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