Catalytic Epoxidation of Enones Mediated by Zinc Alkylperoxide/tert-BuOOH Systems

Abstract

The epoxidation of enones by zinc alkylperoxides is a challenging task receiving considerable attention in contemporary research; however, until now no welldefined zinc alkylperoxide based systems have been described. Here, a new catalytic method of epoxidation of enones in the presence of zinc alkylperoxides supported by N,N-bidentate ligands and tert-butyl hydroperoxide is reported. A new dimeric zinc alkylperoxide complex supported by an aminotroponiminate ligand is also presented. The studied catalytic systems show high activity in the epoxidation of trans-chalcone, and in the case of a chiral catalyst with the (S,S)-N,N′-bis(1-phenylethyl)aminotroponiminate ligand a moderate enantioselectivity was achieved.

New Perspectives for Aminotroponiminates: Coordination Chemistry, Redox Behavior, Cooperativity, and Catalysis

“…Zinc peroxides stabilized by N , N ‐chelating ligands have recently been introduced as well‐defined reagents for the epoxidation of electron deficient alkenes . The catalytic version of these reactions was first realized with zinc ATI catalysts 39 and 40 (or their β‐diketiminate analogs) using trans ‐chalcone ( 37 ) as a model substrate (Scheme ) . Quantitative conversion was reached in 4–8 h at 0 °C.…”

Reaching Milestones in the Oxygenation Chemistry of Magnesium Alkyls: towards Intimate States of O2 Activation and the First Monomeric Well‐Defined Magnesium Alkylperoxide

“…Moreover, we have also emphasized the essential role of the coordination state of the oxygenated organoaluminum and organozinc compounds, as well as the geometric requirements of an O 2 molecule approaching the metal centre . Apart from the fundamental aspects, these systematic studies have advanced rational design of metal alkyl/air systems as radical initiators for organic reactions, stoichiometric and catalytic asymmetric epoxidation of enones and pave the way to well‐defined metal alkoxides (not accessible through the classical alcoholysis path) as potential initiators of cyclic esters polymerization as well as to a new approach for the preparation of semiconductor zinc oxide quantum dots based on organozinc/air systems …”

“…In later studies, the reactions of O 2 with dialkylaluminium and alkylzinc complexes incorporating monoanionic, bidentate ligands allowed for stabilization and subsequent isolation of the first aluminium and zinc alkylperoxides. Since that time, over a dozen examples of metal alkylperoxides with non‐redox‐active metal centres, that is, Li, Na, K, Mg, Zn, Cd, Al, Ga, In incorporating a variety of supporting ligands have been successfully synthesized. These compounds form typically dimeric structures or higher aggregates with bridging alkylperoxide moieties, however, to the best of our knowledge, a handful of examples of terminal metal alkylperoxide have also been described .…”

“…It was not until 1989 when the first dimeric indium [2] and, three years later,g allium [3] alkylperoxides [(tBu) 2 M(m-OOtBu)] 2 were isolated and structurally characterizedf rom the controlled oxygenation of the homoleptic tri(tert-butyl) metald erivatives. In later studies, the reactions of O 2 with dialkylaluminium and alkylzinc complexes incorporating monoanionic, bidentate ligandsa llowedf or stabilizationand subsequent isolation of the first aluminium [4] and zinc [5,6] alkylperoxides.S ince that time, over a dozene xamples of metal alkylperoxides with non-redox-active metalc entres, that is, Li, [7][8][9] Na, [8] K, [8] Mg, [10,11] Zn, [12][13][14][15][16][17] Cd, [18] Al, [19,20] Ga, [21] In [22,23] incorporating av ariety of supporting ligandsh ave been successfully synthesized. These compounds form typicallyd imeric structures or highera ggregates with bridging alkylperoxidem oieties, however,t ot he best of our knowledge,ahandfulo fe xamples of terminal metal alkylperoxide have also been described.…”

“…Moreover,w eh ave also emphasizedt he essential role of the coordination state of the oxygenated organoaluminum [33,34] and organozinc [5,15,16,24] compounds, as well as the geometric requirementso fa nO 2 molecule approachingt he metal centre. [33,34] Apart from the fundamental aspects, these systematic studies have advanced rational designo fm etal alkyl/airs ystemsa sr adicali nitiators for organic reactions, [35][36][37] stoichiometric [38,39] and catalytic asymmetric epoxidation of enones [11,14,40] and pave the way to welldefined metal alkoxides (not accessible through the classical alcoholysis path) as potentiali nitiators of cyclic esters polymerization [25,41] as well as to an ew approach for the preparation of semiconductor zinc oxide quantum dots based on organozinc/ air systems. [42][43][44][45][46] Notably,t he oxygenationc hemistry of magnesium alkyls has remained anu ndeveloped area of research due to difficulties to control the respective reactions ystemsr esulting from the exceptionali nstability of MgOOR species.…”