First Structurally Authenticated Zinc Alkylperoxide: A Model System for the Epoxidation of Enones

Abstract

β‐Ketoiminliganden stabilisieren Zinkkomplexe: Das dimere Zinkalkylperoxid [{(LL)ZnOOEt}2] (LL=HC{(CMe)(2,6‐iPr2C6H3N)}2) wurde isoliert und strukturell charakterisiert (siehe Bild, Zn grün, N blau, O rot, C grau). Der Komplex, der durch Insertion von Disauerstoff in die Zn‐Et‐Bindung gebildet wird, ist hoch aktiv in der Epoxidierung von Enonen.

Alkylzinc Carboxylates as Efficient Precursors for Zinc Oxocarboxylates and Sulfidocarboxylates

“…In a control experiment, a solution of [EtZn(O 2 Ph)] n (1) in THF at 0 8C was treated with an excess of dry dioxygen and the reaction mixture was stirred for approximately five minutes. [6] Based upon the reaction outcome and our recent extensive studies on the oxygenation of alkylzinc complexes, it is reasonable to propose the reaction mechanism shown in Scheme 1 as a working hypothesis. The identity of 2 has been confirmed by X-ray crystallography.…”

“…[1] Zinc oxocarboxylates with the general formula Zn 4 O(O 2 CR) 6 have been known for decades, [2] and interest in them was renewed in the late 1990s primarily by the work of Yaghi and co-workers, who developed the synthesis of metal-organic frameworks (MOFs) with high porosities and tailor-made molecular cavities based on these oxo clusters as secondary building units (SBU). For instance, zinc carboxylates, and particularly alkoxyzinc carboxylates, are attracting a great deal of attention owing to their importance as highly active catalysts for the polymerization or copolymerization of a wide range of organic monomers.…”

“…[4] Our experience in the design, synthesis, and structural characterization of organozinc complexes as models for various transformations [6] prompted us to explore whether alkylzinc carboxylates [7] can be used to synthesize alkoxyzinc carboxylates and other potentially useful clusters. [4] Our experience in the design, synthesis, and structural characterization of organozinc complexes as models for various transformations [6] prompted us to explore whether alkylzinc carboxylates [7] can be used to synthesize alkoxyzinc carboxylates and other potentially useful clusters.…”

“…Compound 1 was characterized by spectroscopic and X-ray singlecrystal studies. [9] In the course of our studies on the role of supporting ligands in the oxygenation of alkylzinc complexes, [6] we have been interested in finding out whether well-defined zinc alkylperoxides or alkoxides can be synthesized by the selective oxygenation of alkylzinc carboxylates. The association of six EtZn(O 2 CPh) molecules results in a tubular structure containing fused networks of twelve-and six-membered heterocycles.…”

Quest for Efficient Catalysts based on Zinc tert‐Butyl Peroxides for Asymmetric Epoxidation of Enones: C2‐ vs C1‐Symmetric Auxiliaries

“…[10] Nevertheless,despite continuous interest in this area, the well-defined Zn-catalyzed highly enantioselective epoxidation of enones remains elusive.In1996, Enders et al [11] reported the first stoichiometric asymmetric epoxidation of a,b-unsaturated ketones mediated by aZ na lkyl peroxide,w hich was generated in situ from Et 2 Zn, (R,R)-N-methylpseudoephedrine and O 2 .U nder such conditions, transchalcone epoxidation was completed in 16 hw ith 61% ee.S ince then, various structurally ill-defined Zn catalysts possessing aB INOLm oiety in combination with tert-butyl hydroperoxide (TBHP) or cumene hydroperoxide (CMHP) have been developed for the catalytic asymmetric epoxidation of av ariety of enones,p roviding the corresponding epoxides in good yields andw ith very high enantiomeric excesses up to 96%. [5a-d] In 2003, our group reported the first structurally authenticated Zn alkyl peroxides [12] and demonstrated that one of them, namely [(BDI)ZnOOEt] 2 (BDI = bdiketiminate ligand), exhibits high efficiency in the stoichiometrice poxidation of trans-chalcone.…”