Chiral N‐Oxides in Asymmetric Catalysis

Abstract

This microreview highlights the utilization of chiral amine N-oxides in catalytic asymmetric transformations, which are discussed in a more general context of catalysis by chiral Lewis bases. Both metal-free and metal-mediated reactions are surveyed.

Novel Chiral Biheteroaromatic Diphosphine Oxides for Lewis Base Activation of Lewis Acids in Enantioselective Allylation and Epoxide Opening

“…[3] Among the different classes of compounds which have been employed as chiral Lewis bases to catalyze the reaction, [4] chiral phosphoramides [5] and pyridine N-oxides [6] have been widely employed with excellent results. Even if systems with relatively easy syntheses were developed, [7] including chiral bispyridine N,N'-dioxides, [8] or simple pyridine N-oxides that are easily assembled from inexpensive amino acids, [9] the search for new, readily available, efficient chiral organocatalysts for the reaction of trichlorosilyl compounds is still a true necessity.…”

Transition Metal‐Catalyzed CH Activation of Indoles

“…An early method exploited Mo catalysis to achieve allylation of electron-rich heterocycles, as reported by Kocovský andc o-workers. [132] A few examples involving indole was disclosed andt wo structural isomers were obtained in either moderate or good yield, depending on the R 1 substituent, (Scheme 62).…”

Highly Enantioselective Synthesis of β‐Heteroaryl‐Substituted Dihydrochalcones Through Friedel–Crafts Alkylation of Indoles and Pyrrole

“…[7][8] Herein, we describe a readily available chiral N,N'-dioxide-scandiumA C H T U N G T R E N N U N G (III) trifluoroA C H T U N G T R E N N U N G methanesulfonate complex system for the enantioselective conjugate addition of indoles and pyrrole to a broad range of chalcones, giving a series of b-heteroarylsubstituted DHCs in moderate to excellent yields (up to 99 %) and high enantioselectivities (up to 92 % ee) using 0.5-10 mol % catalyst loading under mild conditions.…”