Iron-catalyzed asymmetric epoxidation of β,β-disubstituted enones

Zinc complexes formed by 2,2′-bipyridine and 1,10-phenanthroline moieties combined with 2-azanorbornane: modular chiral catalysts for aldol reactions

Zinc complexes of new hybrid chiral imine ligands based on a bicyclic skeleton appear to be effective modular catalysts in asymmetric aldol reactions.

Biologically inspired non-heme iron-catalysts for asymmetric epoxidation; design principles and perspectives

Iron coordination complexes with nitrogen and oxygen donor ligands have long since been known to react with peroxides producing powerful oxidizing species. These compounds can be regarded as simple structural and functional models of the active sites of non-heme iron dependent oxygenases. Research efforts during the last decade have uncovered basic principles and structural coordination chemistry motifs that permit us to control the chemistry that evolves when these iron complexes react with peroxides, in order to provide powerful metal-based, but at the same time selective, oxidising agents. Oxidation methodologies with synthetic value are currently emerging from this approach. The current review focuses on asymmetric epoxidation, a reaction which has large value in synthesis, and where iron/H2O2 based methodologies may represent not only a sustainable choice, but may also expand the scope of state-of-the-art oxidation methods. Basic principles that underlay catalyst design as well as H2O2 activation are discussed, whilst limitations and future perspectives are also reviewed.

Iron(II)-catalyzed asymmetric intramolecular olefin aminochlorination using chloride ion

An iron-catalyzed enantioselective and diastereoselective intramolecular olefin aminochlorination reaction is reported (ee up to 92%, dr up to 15 : 1). In this reaction, a functionalized hydroxylamine and chloride ion are utilized as nitrogen and chlorine sources, respectively. This new method tolerates a range of synthetically valuable internal olefins that are all incompatible with existing asymmetric olefin aminochlorination methods.

A porphyrin-inspired iron catalyst for asymmetric epoxidation of electron-deficient olefins

An in situ formed porphyrin-inspired iron complex that catalyzes asymmetric epoxidation of di- and trisubstituted enones is described. The reaction provides highly enantioenriched α,β-epoxyketones (up to 99% ee). The practical utility of the new catalyst system is demonstrated by the gram-scale synthesis of optically pure epoxide. Hammett analysis suggests that the transition state of the reaction is electron-demanding and the active oxidant is electrophilic.

Alkylation/1,2-aryl migration of α-aryl allylic alcohols with α-carbonyl alkyl bromides using visible-light photoredox catalysis

A visible-light-induced alkene difunctionalization strategy is described for 1,5-dicarbonyl compound synthesis through alkylation and 1,2-aryl migration.

Iron(II)-Catalyzed Asymmetric Epoxidation of Trisubstituted α,β-Unsaturated Esters

An asymmetric epoxidation of trisubstituted α,β-unsaturated esters is described. The oxidation utilizes a pseudo-C₂-symmetric iron(II) catalyst [Fe(L*)₂(CH₃CN)(OTf)](OTf) and peracetic acid as oxidant, yielding the α,β-epoxyesters in high enantiomeric purity (up to 99% ee).

Iron(II)-catalyzed intermolecular amino-oxygenation of olefins through the N-O bond cleavage of functionalized hydroxylamines

An iron-catalyzed diastereoselective intermolecular olefin amino-oxygenation reaction is reported, which proceeds via an iron-nitrenoid generated by the N-O bond cleavage of a functionalized hydroxylamine. In this reaction, a bench-stable hydroxylamine derivative is used as the amination reagent and oxidant. This method tolerates a range of synthetically valuable substrates that have been all incompatible with existing amino-oxygenation methods. It can also provide amino alcohol derivatives with regio- and stereochemical arrays complementary to known amino-oxygenation methods.

Design of novel chiral N,N,O-tridentate phenanthroline ligands and their application to enantioselective addition of organozinc reagents to aldehydes

The novel chiral N,N,O-tridentate ligands (BinThro) containing binaphthyl and phenanthroline units were developed. The enantioselective organozinc addition to aldehydes was performed in the presence of BinThro (S)-1 with up to 95% ee.

Asymmetric epoxidation with H2O2 by manipulating the electronic properties of non-heme iron catalysts

A non-heme iron complex that catalyzes highly enantioselective epoxidation of olefins with H2O2 is described. Improvement of enantiomeric excesses is attained by the use of catalytic amounts of carboxylic acid additives. Electronic effects imposed by the ligand on the iron center are shown to synergistically cooperate with catalytic amounts of carboxylic acids in promoting efficient O-O cleavage and creating highly chemo- and enantioselective epoxidizing species which provide a broad range of epoxides in synthetically valuable yields and short reaction times.

Asymmetric epoxidation of alkenes catalyzed by a porphyrin-inspired manganese complex

A novel strategy for catalytic asymmetric epoxidation of a wide variety of olefins by a porphyrin-inspired chiral manganese complex using H2O2 as a terminal oxidant in excellent yield with up to greater than 99% ee has been successfully developed.

Iron catalyzed asymmetric oxyamination of olefins

The regioselective and enantioselective oxyamination of alkenes with N-sulfonyl oxaziridines is catalyzed by a novel iron(II) bis(oxazoline) complex. This process affords oxazolidine products that can be easily manipulated to yield highly enantioenriched free amino alcohols. The regioselectivity of this process is complementary to that obtained from the analogous copper(II)-catalyzed reaction. Thus, both regioisomers of enantioenriched 1,2-aminoalcohols can be obtained using oxaziridine-mediated oxyamination reactions, and the overall sense of regiochemistry can be controlled using the appropriate choice of inexpensive first-row transition metal catalyst.

Iron-catalyzed intramolecular allylic C-H amination

A highly selective C-H amination reaction under iron catalysis has been developed. This novel system, which employs an inexpensive, nontoxic [Fe(III)Pc] catalyst (typically used as an industrial ink additive), displays a strong preference for allylic C-H amination over aziridination and all other C-H bond types (i.e., allylic > benzylic > ethereal > 3° > 2° ≫ 1°). Moreover, in polyolefinic substrates, the site selectivity can be controlled by the electronic and steric character of the allylic C-H bond. Although this reaction is shown to proceed via a stepwise mechanism, the stereoretentive nature of C-H amination for 3° aliphatic C-H bonds suggests a very rapid radical rebound step.

Iron-Catalyzed Enantioselective Reactions Through the Use of Chiral Bipyridine-Containing Ligands

Recent examples highlighted the use of iron salts in combination with chiral bipyridine-containing ligands for highly enantioselective reactions. Very high enantioselectivities were obtained for various organic transformations, such as oxidation, Mukaiyama aldol and epoxide-opening reactions. These examples represent new entries in the field of green chemistry and sustainable development.