Dinuclear Metal‐ProPhenol Catalysts: Development and Synthetic Applications

Abstract

The ProPhenol ligand is a member of the chiral aza‐crown family that spontaneously forms a bimetallic complex upon treatment with alkyl metal reagents, such as Et2Zn and Bu2Mg. The resulting complex features Lewis acidic and Brønsted basic sites, enabling simultaneous activation of both nucleophile and electrophile in the same chiral environment. Since the initial report in 2000, metal‐ProPhenol catalysts have been used to facilitate a broad range of asymmetric transformations, including aldol, Mannich, and Henry reactions, as well as alkynylations and conjugation additions. By promoting such a diverse array of reactions, these complexes provide rapid and atom‐economical access to valuable complex building blocks. In this Review, we describe in detail the development and synthetic applications of these versatile catalysts with a special focus on recent efforts to improve reactivity and selectivity through ligand design and structural modification.

Zinc‐Catalyzed Asymmetric Hydrosilylation of Cyclic Imines: Synthesis of Chiral 2‐Aryl‐Substituted Pyrrolidines as Pharmaceutical Building Blocks

“…A promising alternative, still unexplored, is to use in the reduction of cyclic imines, an environmentally benign and easily accessible chiral zinc complexes. Inspired by our previous experience in zinc‐catalyzed asymmetric hydrosilylation of ketones [8b,11] and acylic imines, [8a,b,11] in this paper, we present the first example of a highly efficient and enantioselective hydrosilylation of a wide variety of 2‐aryl‐substituted pyrrolines promoted by a Trost‐type zinc complex [12] . Presented concept requires application of the commercially available ProPhenol ligand and is superior to previously published protocols in terms of reaction efficiency and enantioselectivity.…”

Direct Asymmetric α‐Selective Mannich Reaction of β,γ‐Unsaturated Ketones with Cyclic α‐Imino Ester: Divergent Synthesis of Cyclocanaline and Tetrahydro Pyridazinone Derivatives

“…On the basis of the absolute configuration of the products and the previous reports on the mechanism of dinuclear zinc catalysis, [13a–b, 16] a proposed catalytic cycle is depicted in Scheme 3. The dinuclear zinc catalyst C1 e reacts with β,γ‐unsaturated ketones 2 to afford intermediate 9 .…”

Recent Advances in Metal‐Catalyzed Asymmetric Hydroboration of Ketones

“…Motivated by the RE complex-catalyzed enantioselective reductive transformations of carbonyls, [41] very recently, Lu and Zhao utilized the Trost ligand [42] -supported RE [RE = Y, Eu, Nu, La] complexes as a catalyst for asymmetric hydroboration of ketones (Trost ligand = (S,S)-2,6-bis[2-(hydroxyl-diphenylmethyl)-pyrrolidin-1-ylmethyl]-4-methylphenol). [43] These RE complexes were synthesized in good to high yields (M = La (10), 91 %) simply through a stoichiometric reaction of RE[N(SiMe 3 ) 2 ] 3 with Trost ligand in THF.…”