Combining<i>in situ</i>Generated Chiral Silicon Lewis Acid and Chiral Brønsted Acid Catalysts for [3+2] Cycloadditions: Cooperative Catalysis as a Convenient Enantioselective Route to Pyrazolidines
作者:Olga V. Serdyuk、Alexandru Zamfir、Frank Hampel、Svetlana B. Tsogoeva
DOI:10.1002/adsc.201200293
日期:2012.11.12
A facile enantioselective synthesis of chiral pyrazolidines via a [3+2] cycloadditionreaction, involving a BINOL-derived phosphoric acid and an in situ generated BINOL phosphate-derived siliconLewisacid, which may act cooperatively, has been developed.
Silicon Lewis Acid Catalyzed [3+2] Cycloaddition Reactions of Hydrazones/Cyclopentadiene: Mild Access to Pyrazolidine Derivatives
作者:Alexandru Zamfir、Sebastian Schenker、Walter Bauer、Timothy Clark、Svetlana B. Tsogoeva
DOI:10.1002/ejoc.201100206
日期:2011.7
A first and fairly mild metal-free catalytic route was developed for the [3+2] cycloadditions of different N-acylhydrazones to cyclopentadiene, providing the synthetically andbiologically important five-membered cyclic compounds pyrazolidines. The reaction was successfully conducted in high yields (up to 99 %) with high diastereoselectivities (up to 98:2 dr) by using catalytic amounts of TMSOTf (trimethylsilyl
Asymmetric Hydrocyanation of Hydrazones Catalyzed by in Situ Formed <i>O</i>-Silylated BINOL-Phosphate: A Convenient Access to Versatile α-Hydrazino Acids
作者:Alexandru Zamfir、Svetlana B. Tsogoeva
DOI:10.1021/ol9025974
日期:2010.1.1
A first organocatalytic enantioselective route was developed for the conversion of readily prepared and air stable aliphatic hydrazones to synthetically valuable alpha-hydrazinonitriles. This BINOL-phosphate catalyzed Strecker-type reaction (see scheme, Ar = p-NO2-Ph) provides a new practical and direct route to alpha-hydrazino acids of synthetic and biological importance. The actually active catalyst is proposed to be an In situ formed O-silylated BINOL-phosphate, thus shifting the nature of catalysis from Bronsted acid to Lewis acid organocatalysis.