Catalytic Asymmetric Aziridination of α,β‐Unsaturated Aldehydes

Rhodium(II)-Catalyzed Enantioselective Intermolecular Aziridination of Alkenes

C₄-Symmetrical dirhodium(II) tetracarboxylates are highly efficient catalysts for the asymmetric intermolecular aziridination of substituted alkenes with sulfamates. The reaction proceeds with high levels of efficiency and chemoselectivity to afford aziridines with excellent yields of up to 95% and enantiomeric excesses of up to 99%. The scope of the alkene aziridination includes mono-, di-, and trisubstituted olefins as well as the late-stage functionalization of complex substrates. The reaction can be performed on a gram-scale with a catalyst loading of 0.1 mol %. Our DFT study led us to propose a two-spin-state mechanism, involving a triplet Rh-nitrene species as key intermediate to drive the stereocontrolled approach and activation of the substrate.

A practical method for the aziridination of α,β-unsaturated carbonyl compounds with a simple carbamate utilizing sodium hypochlorite pentahydrate

The efficient formation of tert-butyl N-chloro-N-sodio-carbamate by the reaction of simple tert-butyl carbamate with sodium hypochlorite pentahydrate (NaOCl·5H₂O) would be a practical and green method for the aziridination of α,β-unsaturated carbonyl compounds. The process described herein is transition-metal free, all of the materials are commercially available, the byproducts (NaCl and H₂O) are environmentally benign and the reaction is stereoselective. The resulting aziridines are potential precursors of amino acids.

Electrophilic Aminating Agents in Total Synthesis

Classical amination methods involve the reaction of a nitrogen nucleophile with an electrophilic carbon center; however, in recent years, umpoled strategies have gained traction where the nitrogen source acts as an electrophile. A wide range of electrophilic aminating agents are now available, and these underpin a range of powerful C−N bond‐forming processes. In this Review, we highlight the strategic use of electrophilic aminating agents in total synthesis.

Stereoselective synthesis of trans-aziridines via intramolecular oxidative C(sp3)–H amination of β-amino ketones

An expedient strategy for the synthesis of trans-2,3-disubstituted via the intramolecular KI/TBHP mediated oxidative dehydrogenative C(sp³)–H amination reaction was presented.

Total Synthesis of (-)-Salinosporamide A via a Late Stage C-H Insertion

The synthesis of (-)-salinosporamide A, a proteasome inhibitor, is described. The synthesis highlights the assembly of a densely decorated pyrrolidinone core via an aza-Payne/hydroamination sequence. Central to the success of the synthesis is a late-stage C-H insertion reaction to functionalize a sterically encumbered secondary carbon. The latter functionalization leads to an enabling transformation where most of the prototypical strategies failed.

Organocatalytic Olefin Aziridination via Iminium-Catalyzed Nitrene Transfer: Scope, Limitations, and Mechanistic Insight

Olefin aziridination via organocatalytic nitrene transfer offers potential complementarity to metal-catalyzed methods; however there is a lack of reports of such reactions in the literature. Herein is reported a method that employs an iminium salt to catalyze the aziridination of styrenes by [ N-( p-toluenesulfonyl)imino]phenyliodinane (PhINTs). These reactions are hypothesized to proceed via a diaziridinium salt as the active oxidant. In addition to outlining the scope and limitations of the method, evidence for a polar, stepwise mechanism is presented, which provides new insight into the nature of iminium catalysis of nitrene transfer.

Fluorinated triazole-containing sphingosine analogues. Syntheses and in vitro evaluation as SPHK inhibitors

Sphingosine analogues with a rigid triazole moiety in the aliphatic chain and systematic modifications in the polar head and different degrees of fluorination at the terminus of the alkylic chain were synthesized from a common alkynyl aziridine key synthon. This key synthon was obtained by enantioselective organocatalyzed aziridination and it was subsequently ring opened in a regioselective manner in acidic medium. Up to 16 sphingosine analogues were prepared in a straightforward manner. The in vitro activity of the obtained products as SPHK1 and SPHK2 inhibitors was evaluated, displaying comparable activity to that of DMS.

Step economy strategy for the synthesis of amphoteric aminoaldehydes, key intermediates for reduced hydantoins

Despite of the orthogonal reactivity of the N–H aziridines aldehyde, these compounds exist as an equilibrium of three different forms – whereas the dimeric one is mostly observed in a variety of solvents. In this work, we have developed an alternative protocol for the aminoaldehyde dimers synthesis in two steps starting with an organocatalyzed aziridination between α,β-unsaturated aldehydes and a protected amine to afford known isolable and stable N-protected aziridine aldehydes. After Boc-deprotection, dimeric species were immediately formed from monomeric N–H aziridine aldehydes. From this building-block new reduced hydantoins were prepared via [3+2]-annulation with isocyanates.

Organocatalytic Synthesis of cis-2,3-Aziridine Aldehydes by a Postreaction Isomerization

An unprecedented organocatalytic cis-selective aziridination of α,β-unsaturated aldehydes is described. The strategy utilizes postreaction isomerization as a key step. Our study demonstrates that by a proper choice of structural features of reagents and the catalyst the outcome of well-established reactions can be altered, leading to the formation of normally inaccessible diastereomers. The usefulness of the developed approach has been confirmed in the syn-selective formal aminohydroxylation of α,β-unsaturated aldehydes.

Origin of Life and the Phosphate Transfer Catalyst

In this paper, we revisit several issues relevant to origin-of-life research and propose a Phosphate Transfer Catalyst hypothesis that furthers our understanding of some of the key events in prebiotic chemical evolution. In the Phosphate Transfer Catalyst hypothesis, we assume the existence of hypothetical metallopeptides with phosphate transfer activity that use abundant polyphosphates as both substrates and energy sources. Nonspecific catalysis by this phosphate transfer catalyst would provide a variety of different products such as phosphoryl amino acids, nucleosides, polyphosphate nucleotides, nucleic acids, and aminoacylated nucleic acids. Moreover, being an autocatalytic set and metabolic driver at the same time, it could possibly replicate itself and produce a collective system of two polymerases; a nucleic acid able to catalyze peptide bond formation and a peptide able to polymerize nucleic acids. The genetic code starts at first as a system that reduces the energy barrier by bringing substrates (2'/3' aminoacyl-nucleotides) together, an ancestral form of the catalysis performed by modern ribosomes. Key Words: Origin of life-Prebiotic chemistry-Catalysis-Nucleic acids. Astrobiology 17, 277-285.

Efficient Access to Chiral Trisubstituted Aziridines via Catalytic Enantioselective Aza-Darzens Reactions

Herein, we report a Zn-ProPhenol catalyzed aza-Darzens reaction using chlorinated aromatic ketones as nucleophilic partners for the efficient and enantioselective construction of complex trisubstituted aziridines. The α-chloro-β-aminoketone intermediates featuring a chlorinated tetrasubstituted stereocenter can be isolated in high yields and selectivities for further derivatization. Alternatively, they can be directly transformed to the corresponding aziridines in a one-pot fashion. Of note, the reaction can be run on gram-scale with low catalyst loading without impacting its efficiency. Moreover, this methodology was extended to α-bromoketones which are scarcely used in enantioselective catalysis because of their sensitivity and lack of accessibility.

Synthetic Study of Pactamycin: Enantioselective Construction of the Pactamycin Core with Five Contiguous Stereocenters

A synthetic study of pactamycin is described. Enantioselective construction of the aminocyclopentitol core of pactamycin bearing five contiguous stereocenters was achieved based on an organocatalytic asymmetric aziridination of 2-cyclopentene-1-one, a regio- and diastereoselective 1,3-dipolar cycloaddition, and a rhodium-catalyzed C-H amination reaction.

Catalytic cross-benzoin/Michael/acetalization cascade for asymmetric synthesis of trifluoromethylated γ-butyrolactones

A sequential NHC-amine catalytic cascade reaction has been developed. This approach incorporates a highly chemoselective intermolecular cross-benzoin reaction and a highly regioselective Michael-acetalization cascade.

Combined heterogeneous metal/organic catalysts for eco-friendly synthesis

The interplay and synergistic cooperation between homogeneous and heterogeneous catalyst systems is of utmost importance in nature. It is also applied in chemical synthesis. Here, it can allow for new reactivity, which is not possible by the employment of a single catalyst, and promote the catalysis of multiple transformations in a one-pot sequence. This could overall lead to novel reactions and the development of sustainable chemistry. In this context, a versatile and broad synergistic strategy for the selective synthesis of valuable molecules with variable complexity and under eco-friendly conditions is disclosed. It is based on integrated heterogeneous metal/organo multiple relay catalysis, which is performed in a single reaction vessel, and allows for the assembly of complex molecules (e.g., heterocycles and carbocycles) with up to three quaternary stereocenters in a highly enantioselective fashion from simple alcohols and air/O2.

An unprecedented base-promoted domino reaction of methyleneindolinones and N-tosyloxycarbamates for the construction of bispirooxindoles and spiroaziridine oxindoles

An efficient and unprecedented domino reaction of methyleneindolinones andN-tosyloxycarbamates was realized to construct bispirooxindoles and spirooxindole aziridines.

Organocatalytic asymmetric remote aziridination of 2,4-dienals

Highly regio- and stereoselective remote aziridination of 2,4-dienals has been developed, based on a vinylogous iminium-ion-dienamine catalytic cascade reaction. Transformations of the aziridine products into enantioenriched motifs are also demonstrated. Furthermore, the reaction concept is extended to include enantioselective 1,6-addition of thiols.

Enantioselective aziridination of cyclic enals facilitated by the fluorine-iminium ion gauche effect

The enantioselective, organocatalytic aziridination of small, medium and macro-cyclic enals is reported using (S)-2-(fluorodiphenyl methyl)-pyrrolidine. Central to the reaction design is the reversible formation of a β-fluoroiminium ion intermediate, which is pre-organised on account of the fluorine-iminium ion gauche effect. This conformational effect positions the fluorine substituent synclinal-endo to the electropositive nitrogen centre thus benefiting from favourable stereoelectronic and electrostatic interactions (σC-H →σC-F *; F(δ-…︁) N(+) ). Consequently, one of the shielding groups on the fluorine-bearing carbon atom is positioned above the π-system, forming the basis of an enantioinduction strategy. Treatment of this intermediate with a "nitrene" source furnished a series of novel, optically active aziridines (e.r. up to 99.5:0.5). Further derivatisation of the product aziridines gives facile access to various amino acid derivatives, including β-fluoroamino acids. Crystallographic analyses of both the aziridines and their derivatives are disclosed.

Enantioselective approach to quinolizidines: total synthesis of cermizine D and formal syntheses of senepodine G and cermizine C

The formal syntheses of C5-epi-senepodine G and C5-epi-cermizine C have been accomplished through a novel diastereoselective, intramolecular amide Michael addition process. The total synthesis of cermizine D has been achieved through use of an organocatalyzed, heteroatom Michael addition to access a common intermediate. Additional key steps of this sequence include a matched, diastereoselective alkylation with an iodomethylphenyl sulfide and sulfone-aldehyde coupling/reductive desulfurization sequence to combine the major subunits. The utility of a Hartwig-style C-N coupling has been explored on functionally dense coupling partners. Diastereoselective conjugate additions to α,β-unsaturated sulfones have been investigated, which provided the key sulfone intermediate in just six steps from commercially available starting materials. The formal syntheses of senepodine G and cermizine C have been accomplished through an intramolecular cyclization process of a N-Boc-protected piperidine sulfone.