The Jørgensen–Hayashi catalyst [(S)-α,α-diphenylprolinol trimethylsilyl ether] was grafted onto the surface of two different supports: phosphorus dendrimers (generations 1 to 3) and magnetic, polymer-coated cobalt/carbon (Co/C) nanobeads. These new supported catalysts displayed high activities and selectivities in the Michael additions of a wide range of aldehydes to different nitroolefins. Moreover, the dendrimer of the third generation displayed excellent recycling abilities since it could be recovered and reused in 7 consecutive runs without loss of activity.

The tris(acetylacetonato)rhodium(III) catalyst is shown to be a versatile catalyst in the presence of DABCO (1,4-diazabicyclo[2.2.2]octane) as ligand for the α-alkylation of ketones followed by transfer hydrogenation, for the one-pot β-alkylation of secondary alcohols with primary alcohols and for the alkylation of aromatic amines in the presence of an inorganic base in toluene.

A novel concept for the direct oxidation of cycloalkanes to the corresponding cyclic ketones in a one-pot synthesis in water with molecular oxygen as sole oxidizing agent was reported recently. Based on this concept we have developed a new strategy for the double oxidation of n-heptane to enable a biocatalytic resolution for the direct synthesis of heptanone and (R)-heptanols in a one-pot reaction. The bicatalytic cascade employs an NADH driven P450 BM3 monooxygenase variant (WT^NADH, 19A12^NADH or CM1^NADH) and an (S)-enantioselective alcohol dehydrogenase (RE-ADH). In the initial step n-heptane is hydroxylated under consumption of NADH to produce (R/S)-heptanol. In the second oxidation step the (S)-heptanol enantiomers are transformed to the corresponding ketones, reducing and thereby regenerating the cofactor. Characterization of initial hydroxylation step revealed high turnover frequencies (TOF) of up to 600 min⁻¹, as well as high coupling efficiencies using NADH as cofactor (up to 44%). In the cascade reaction a nearly 2-fold improved product formation was achieved, compared to the single hydroxylation reaction. The total product concentration reached 1.1 mM, corresponding to a total turnover number (TTN) of 2500. Implementation of an additional cofactor regeneration system (D-glucose/glucose dehydrogenase) enabled a further enhancement in product formation with a total product concentration of 1.8 mM and a TTN of 3500.

This paper describes a new convergent approach to the synthesis of an HIV protease inhibitor which was designed to be suitable in long acting formulations. Unique features in the synthesis include an asymmetric hydrogenation as well as enzymatic reduction of a key chloro ketone intermediate, to set the threo stereochemistry in the corresponding epoxide and the diastereoselective coupling of the latter with the zinc enolate of a suitable functionalized amide derivative.

Catalysis of the challenging cycloaddition of carbon dioxide to internal epoxides has been studied using iron(III) amine triphenolate complexes and particular focus has been given to the stereochemical regulation of this process. When pure cis- or trans-2,3-epoxybutane is used as substrate, the stereochemistry of the product can be controlled yielding selectively cis- or trans-cyclic carbonates for both epoxidic substrates. This stereochemical divergence relates to two accessible catalytic pathways leading to either the cis or trans product via two distinct ring-closure steps. The involved mechanism and stereocontrol is a function of the catalyst/co-catalyst loading, and is further influenced by the medium, temperature and catalyst/co-catalyst structure. Other trans-internal epoxides could also be successfully converted into the pure trans-cyclic carbonate products without any loss of stereochemical information.

The reductive amination of ketones to produce chiral amines is an important transformation in the production of pharmaceutical intermediates. Therefore, industrially applicable enzymatic methods that enable the selective synthesis of chiral amines could be very useful. Using a phenylalanine dehydrogenase scaffold devoid of amine dehydrogenase activity, a robust amine dehydrogenase has been evolved with a single two-site library allowing for the direct production of (R)-1-(4-fluorophenyl)-propyl-2-amine from para-fluorophenylacetone with a k_cat value of 6.85 s⁻¹ and a K_M value of 7.75 mM for the ketone substrate. This is the first example of a highly active amine dehydrogenase capable of accepting aliphatic and benzylic ketone substrates. The stereoselectivity of the evolved amine dehydrogenase was very high (>99.8% ee) showing that high selectivity of the wild-type phenylalanine dehydrogenase was conserved in the evolution process. When paired with glucose/glucose dehydrogenase, NADH cofactor can be effficiently regenerated and the reaction driven to over 93% conversion. The broad specificity, high selectivity, and near complete conversion render this amine dehydrogenase an attractive target for further evolution toward pharmaceutical compounds and subsequent application.

Glucose dehydrogenase (GDH) is frequently used for the reduction of NAD⁺ and NADP⁺ in bench- and industrial-scale syntheses because the coenzyme regenerating system GDH is easy to apply, robust and relatively inexpensive. To optimize the application of this long known coenzyme regeneration system we investigated the commonly applied Bacillus GDH and characterized this enzyme by its kinetic features in the presence of substrates and products at pH 6.4 and 8.0. Three substrates/products were found to inhibit GDH considerably: (i) the reaction product glucono-1,5-lactone, (ii) the reduced coenzyme NAD(P)H and (iii) the oxidized coenzyme NAD(P)⁺. The inhibition of GDH under several process conditions was modeled using the determined kinetic constants. It was found that the GDH regeneration system is strongly inhibited by the usually applied conditions. This study provides the rate equation of the GDH reaction and simulations of this coenzyme regenerating system leading to an improved prediction and, thus, to a faster scale-up and increased efficiency of NAD(P)H-dependent synthetic processes.

A modular library of readily available phosphite-pyridine ligands has been successfully applied for the first time in the iridium-catalyzed asymmetric hydrogenation of a broad range of minimally functionalized olefins. The modular ligand design has been shown to be crucial in finding highly selective catalytic systems for each substrate. Excellent enantioselectivities (ees up to 99%) have therefore been obtained in a wide range of E- and Z-trisubstituted alkenes, including more demanding triaryl-substituted olefins and dihydronaphthalenes. This good performance extends to the very challenging class of terminal disubstituted olefins, and to olefins containing neighbouring polar groups (ees up to 99%). Both enantiomers of the reduction product can be obtained in excellent enantioselectivities by simply changing the configuration of the carbon next to the phosphite moiety. The hydrogenations were also performed using propylene carbonate as solvent, which allowed the iridium catalyst to be reused and maintained the excellent enantioselectivities.

Both enantiomers of optically pure 4-bromo-3-hydroxybutanoate, which is an important chiral building block in the syntheses of various biologically active compounds including statins, were synthesized from rac-4-bromomethyl-β-lactone through kinetic resolution. Candida antarctica lipase B (CAL-B) enantioselectively catalyzes the ring opening of the β-lactone with ethanol to yield ethyl (R)-4-bromo-3-hydroxybutanoate with high enantioselectivity (E>200). The unreacted (S)-4-bromomethyl-β-lactone was converted to ethyl (S)-4-bromo-3-hydroxybutanoate (>99% ee), which can be further transformed to ethyl (R)-4-cyano-3-hydroxybutanoate, through an acid-catalyzed ring opening in ethanol. Molecular modeling revealed that the stereocenter of the fast-reacting enantiomer, (R)-bromomethyl-β-lactone, is ~2 Å from the reacting carbonyl carbon. In addition, the slow-reacting enantiomer, (S)-4-bromomethyl-β-lactone, encounters steric hindrance between the bromo substituent and the side chain of the Leu278 residue, while the fast-reacting enantiomer does not have any steric clash.

The C-terminal activation of peptides as prerequisite for the formation or ligation of peptide fragments is often associated with the problem of epimerization. We report that ruthenium-catalyzed alkyne addition with (+)-2,3-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane as ligand allows the racemization-free synthesis of peptide enol esters tolerating a wide range of functional groups. The transformation can be performed in a variety of different solvents addressing the solubility issues imposed by peptides with varying amino acid side chain patterns. We show that peptide enol esters with an amide motif in the enol moiety are excellent acyl donors for the peptide condensation with other peptide fragments in organic solvents using serine endopeptidase subtilisin A as catalyst. The reported combination of transition metal catalysis with enzymatic peptide ligations adds an important tool for the racemization-free synthesis and ligation of peptides which is compatible even with unprotected amino acid side chains.

Prochiral bicyclic diketones were transformed to a single diastereomer of 3-substituted cyclohexylamine derivatives via three consecutive biocatalytic steps. The two chiral centres were set up by a CC hydrolase (6-oxocamphor hydrolase) in the first step and by an ω-transaminase in the last step. The esterification of the intermediate keto acid was catalysed by a lipase in the second step if possible. For two substrates the CC hydrolytic step as well as the esterification could be run simultaneously in a one-pot cascade in an organic solvent. In one example, the reaction mixture of the first two steps could be directly subjected to bio-amination in an organic solvent without the need to change the reaction medium. Depending on the choice of the ω-transaminase employed and the substrate the cis- as well as the trans-diastereomers could be obtained in optically pure forms.

Direct and regiospecific amino-functionalization of non-activated carbon could be achieved using one recombinant microbial catalyst. The presented proof of concept shows that heterologous pathway engineering allowed the construction of a whole-cell biocatalyst catalyzing the terminal amino-functionalization of fatty acid methyl esters (e.g., dodecanoic acid methyl ester) and alkanes (e.g., octane). By coupling oxygenase and transaminase catalysis in vivo, both substrates are converted with absolute regiospecificity to the terminal amine via two sequential oxidation reactions followed by an amination step. Such demanding chemical three-step reactions achieved with a single catalyst demonstrate the tremendous potential of whole-cell biocatalysts for the production of industrially relevant building blocks.

The β-fructofuranosidase (Ffase) from Schwanniomyces occidentalis (Ffase-Leu196 variant) was subjected to four cycles of directed evolution to enhance the transglycosylation activity for the synthesis of β-(2→6) linked fructooligosaccharides (FOS). With a 5.5-fold improvement in fructose transferase activity over the parental type and greater selectivity for the synthesis of 6-kestose (up to 73% of the total FOS), the mutants doubled FOS synthesis to 168 g L.⁻¹ Whilst the F523V and H510P mutations were located at the C-terminus of the protein, mutations Q78L and I203L were associated with the acidic catalytic triad where they modified its interactions with the surrounding residues, in turn varying the hydrolase and transferase rates.

The novel rhodium complex [Rh(S)-Phanephos(cod)]-catalyzed hydrogenation of disubstituted (E)-enol acetate carboxylic acids is reported. The catalytic cycle works under 30 bar of hydrogen under conventional heating giving different 3-acetoxy-2,3-disubstituted carboxylic acids with ee ≥90%. Hydrogenation occurred also under microwave dielectric heating without eroding the enantioselectivity but improving the overall efficiency of the process. With microwaves, hydrogen pressure and reaction time required for complete hydrogenation dropped to 5 bar and 30 min, respectively. The best performance of this catalyst under microwave irradiation was TON 100, TOF 196 h⁻¹ with ee 99% on a 6-g scale.

The modular nature of the BIPI ligands allows for systematic optimization of each ligand region. The development of ligands optimized for asymmetric hydrogenation of the challenging unfunctionalized olefin substrate class is described. The naphthyl peri position, C-8, has been identified as a critical stereocontrol element in the design of these ligands. Highly enantioselective ligands suitable for hydrogenation of tri- and tetrasubstituted olefins are detailed.

α′-Fluoro β-boryl ketones can be efficiently synthesised from a sequential organocatalytic β-boration pathway and consecutive electrophilic fluorination reaction in an acidic medium. Alternatively, the regioisomers of α-fluoro β-boryl ketones can be diastereoselectively obtained from Cu(I)-mediated β-boration followed by in situ fluorination of the boron enolate. Enantioenriched mixtures of the major anti-diastereomer of vicinal CB and CF bonds are found in the presence of the chiral ligand QuinoxP*.

An efficient method for synthesis of the widely applicable 2-substituted benzothiazoles has been developed. The process requires only 0.1 mol% [Ru(bpy)₃Cl₂], O₂, and visible light irradiation with substrates: 2-aminothiophenol and a variety of aldehydes. We established an oxidative quenching of the photoredox catalyst as being the key process in this photoelectrocatalytic cycle.

Triarylsulfonium salts are prompted to undergo efficient homolytic reduction by single electron transfer under mild photocatalytic conditions. The liberated aryl radical can then participate in carbon-carbon bond formation processes with allyl sulfones and activated olefins. Triarylsulfonium salts emerge as a valuable and alternative source of aryl radicals for synthesis.

A visible light-induced, aerobic oxyamidation reaction of indoles, using air as the sole oxidant, has been developed. This process serves as a photocatalytic strategy to generate efficiently tetrahydro-5H-indolo[2,3-b]quinolinols, which may have interesting biological and pharmacological activities owing to their privileged indoline structure.

An oxidative cross-coupling reaction between aldehydes and sulfoximines involving dual CH/NH functionalization has been developed. This reaction process is facilitated by a simple copper catalyst (1 mol% loading) and tert-butyl hydroperoxide (TBHP) as the oxidant and proceeds under mild reaction conditions to afford a series of valuable N-acylated sulfoximine derivatives in excellent yields.

A copper-catalyzed amination of aryl halides with nitriles has been developed. The use of nitriles as nitrogen nucleophiles can make the synthesis of N-arylamides more simple than that using amides through in-situ hydrolysis. A variety of N-arylamides and benzoxazole derivatives can be synthesized according to this approach.

Herein we describe a direct, multicomponent assembly of 1,5-enynes. The titanocene-catalyzed coupling of an aryl aldehyde, iodoalkyne, and allylsilane enables the convergent and rapid synthesis of this versatile architectural motif in good to excellent yields.

The first organocatalytic Mannich reaction of 5H-oxazol-4-ones with various readily prepared aryl- and alkylsulfonimides has been developed. Two commercially available pseudoenantiomeric Cinchona alkaloids-derived tertiary amine/ureas have been demonstrated as the most efficient catalysts to access the opposite enantiomers of the Mannich products with equally excellent enantio- and diastereoselectivities. From the Mannich adducts, important α-methyl-α-hydroxy-β-amino acid derivatives, such as the α-methylated C-13 side chain of taxol and taxotere, can be conveniently prepared.

An efficient and practical synthetic method has been developed for the preparation of 3-vinylindoles by the direct CH olefination of indoles with alkenes. The transformation is catalyzed by palladium acetate combined with 12-molybdophosphoric acid and uses oxygen as the terminal oxidant. 4-Dimethylaminopyridine (DMAP) was observed to be an effective additive for the olefination reaction. Functional groups such as methoxy, benzyloxy, fluoro, bromo, ester, phenyl, and methyl were tolerated under the reaction conditions.

An efficient palladium-catalyzed decarboxylative ortho-acylation of 2-aryloxypyridines with α-oxocarboxylic acids is described. In this new transformation, the aromatic C(sp²)H bond was successfully acylated to give diverse aromatic ketones regioselectively in moderate to good yields. The pyridine group can be removed easily after the acylation to give the corresponding 2-hydroxy aromatic ketones.

Some readily available Boc-protected 2-(3-methoxy-1-propynyl)anilines and nitrones in platinum-catalyzed reactions deliver [1,2]oxazino[5,4-b]indoles. Twelve examples with yields of 41–95% are reported. Different substituents like nitro, trifluoromethyl, fluoro, bromo, and ester groups are tolerated. With regard to the mechanism, this reaction probably combines an initial intramolecular cyclization/elimination to vinylcarbenoid species and a subsequent stepwise intermolecular [3+3] cycloaddition with the nitrones.

An efficient and simple deuteration method of arenes using the platinum on carbon-isopropyl alcohol-cyclohexane-deuterium oxide combination under hydrogen gas-free conditions was accomplished. Since the hydrogen–deuterium exchange reaction cannot be promoted without isopropyl alcohol, zerovalent platinum metal (on carbon) is self-activated by the in situ-generated very low amount of hydrogen or hydrogen–deuterium gas derived from isopropyl alcohol or isopropyl alcohol-d₁. Deuterium-labeled compounds with high deuterium contents can be easily isolated by the filtration of platinum on carbon and simple extraction. The present hydrogen gas-free method is safe from the viewpoint of process chemistry and various arenes possessing a variety of reducible functionalities within the molecule could be effectively and directly deuterium-labeled without undesired reduction.

Acetylenes undergo the [4+2] cycloaddition to 3,6-di(pyrrol-2-yl)-1,2,4,5-tetrazine in the potassium hydroxide/dimethyl sulfoxide or potassium tert-butoxide/dimethyl sulfoxide systems (80 °C, 2.5–4 h) to afford (after extrusion of the nitrogen molecule from the intermediate) 3,6-di(pyrrol-2-yl)pyridazines in up to 73% yield, while under non-catalytic conditions this reaction does not take place. This unusual result substantially extends the scope of synthetic application and mechanistic diversity of the Diels–Alder reaction. The step-wise mechanisms involving the formation of [OH/tetrazine]⁻ or [t-BuO/tetrazine]⁻ anionic intermediate complexes or cycloaddition of tetrazine to the acetylide anion are considered.

On the terminal diazo nitrogen atom, two CN bonds are formed in the bicyclization reaction of the readily available acyclic substrates with diazomethanes as 1,3-dipoles. The tandem 1,3-dipolar cycloaddition/intramolecular aza-addition/oxidative aromatization reaction can tolerate a variety of functional groups and proceeds under mild metal-free conditions to give substituted analogues of withasomnine alkaloids in good to high yields in a single step.

Silver-catalyzed stereoselective [3+2] cycloadditions between mono-substituted cyclopropyl-indanimines and aldehydes are reported. The stereochemical course of the reaction is rationalized with a cyclic transition state. The resulting indanimine cycloadducts are not readily hydrolyzed unless external aldehydes are present with the silver catalyst. Notably, this hydrolysis process leads to a change of stereochemistry for the resulting indanone products.

A convenient and efficient functionalization of polyhaloaromatics via regioselective magnesiation has been developed. Starting from simple, inexpensive but structurally challenging arenes, metallation by magnesium amide bases was achieved under mild conditions. The desired Grignard reagents were stable towards aryne formation, were obtained in good yields within short reaction times and could be reacted with a variety of typical electrophiles, providing attractive, functionalized building blocks in good to excellent yields. As an application we have prepared the antimicrobial natural product 2,6-dichloro-3-phenethylphenol isolated from the New Zealand liverwort Riccardia marginata. This synthesis involves a mixed bimetallic compound prepared via metallation of a phenylboronic acid pinacol ester derivative and subsequent selective cross-coupling.

A current trend in organic chemistry is the development of highly efficient, environmentally friendly and inexpensive catalysts for asymmetric transformations. Alkaline earth metals, due to their specific chemical properties and abundance in nature, provide promising and challenging catalysts in organic synthesis. This article describes the utilization of alkaline earth metals in the development of an effective catalytic system based on calcium salts in combination with Box-type ligands. We disclose asymmetric 1,4-addition and [3+2] cycloaddition reactions using simple catalytic systems consisting of calcium chloride dihydrate, chiral ligands and tetramethylguanidine. Various Box ligands were synthesized and the most effective proved to be that bearing an indane chiral backbone and a cyano group. Depending on the structure of both glycine Schiff bases and α,β-unsaturated compounds, the corresponding Michael adducts or pyrrolidine derivatives were obtained in moderate to high yields with high enantioselectivities. Modification of the catalytic system by using more Lewis acidic calcium salts such as calcium triflate and neutral Pybox-type ligands allows a tuning of the chemoselectivity and leads to suppression of the [3+2] cycloadition reactions. Various β-substituted acrylates provided 1,4-addition adducts exclusively in high yields with moderate to high diastereo- and enantioselectivities. This methodology has broadened a synthetic route to β-branched glutamic acid derivatives and established calcium salts as useful and attractive catalysts for asymmetric catalysis.

A general and convenient palladium-catalyzed oxidative Heck arylation of both N-protected and N,N-diprotected allylic amines with arylboronic acids under mild conditions has been developed. The catalyst system, consisting of Pd(OAc)₂ (palladium acetate), AgOAc (silver acetate) and KHF₂ (potassium hydrogen fluoride), could efficiently catalyze the coupling reaction in acetone without the aid of any ligand, leading exclusively to the γ-arylated allylic amine products in good to excellent yields. This method is highlighted with excellent regio- and stereocontrol and remarkable functional group tolerance. The carbamate moiety in allylic amine substrates is of crucial importance to the catalytic performance, and the chelation between the carbonyl O (oxygen) and Pd (palladium) atoms is believed to be responsible for the high regioselectivity and stereoselectivity observed.

A palladium-catalyzed reaction of 2-alkynylaniline, isocyanides, and silver acetate is described, leading to 3-amidylindoles in moderate to good yields. During the process, five new bonds are formed with high reaction efficiency in one-pot procedure.

The tandem gold-catalyzed hydrosilyloxylation–aldol and hydrosilyloxylation–Mannich reactions were developed through the formation of an enol silyl ether catalytically generated in situ from alkynylaryloxysilanols in the 6-exo mode in one reaction vessel.

An efficient catalytic asymmetric hydrogenation of racemic α-arylcyclohexanones with an ethylene ketal group at the 5-position of the cyclohexane ring via dynamic kinetic resolution has been developed, giving chiral α-arylcyclohexanols with two contiguous stereocenters with up to 99% ee and >99:1 cis/trans-selectivity. Using this highly efficient asymmetric hydrogenation reaction as a key step, (−)-α-lycorane was synthesized in 19.6% overall yield over 13 steps from commercially available starting material.

The first catalytic asymmetric five-component tandem reactions of β-keto esters, aromatic aldehydes and anilines have been established in the presence of a chiral phosphoric acid, affording densely functionalized tetrahydropyridines with concomitant generation of five σ bonds and two stereogenic centers in high diastereo- and enantioselectivities (up to >99:1 dr, 95:5 er). In addition, the first isolation and preparation of a diene species as the key intermediate of the reaction has been successfully realized, leading to the formation of the desired tetrahydropyridine via further condensation with in situ generated imine, which supported the proposed tandem [4+2] reaction pathway to some extent. This protocol not only represents the first enantioselective example of this five-component tandem reaction, but also provides an unprecedented access to enantioenriched tetrahydropyridines with structural diversity, which holds great potential in medicinal chemistry.

The development of a novel heterogeneous catalytic asymmetric cascade reaction for the synthesis of tetrahydroquinolines from 2-nitrophenylpyruvates is reported. Optically enriched 3-hydroxy-3,4-dihydroquinolin-2(1H)-ones are prepared by enantioselective hydrogenation of the activated keto group over a Cinchona alkaloid-modified Pt catalyst, reduction of the nitro group and spontaneous cyclization cascade. Acceleration of the enantioselective hydrogenation of the activated keto group over the catalyst modified by Cinchona alkaloids ensured high tetrahydroquinolinone selectivities. The scope of the reaction was checked using twelve substrates. Both yields and enantioselectivities were significantly influenced by the nature and position of the substituents on the phenyl ring. Substituents adjacent to the nitro group considerably increased the product yield, due to their effect on the nitro group′s reduction rate; however, had only a limited effect on enantioselectivities.

Herein, we report a detailed study on the electrophilic alkynylation of cyclic keto esters and amides with ethynylbenziodoxolone (EBX) reagents. The structure and stability of this class of reagents is first described more in details. Differential scanning calorimetry (DSC) experiments showed a strong exothermic decomposition with EBX reagents, leading to guidelines for the safe use of these compounds. The extension of the method to aromatic alkynes and a broad range of benziodoxol(on)e reagents is then reported. Based on our preliminary results using Cinchona-based phase-transfer catalysts, the enantioselective alkynylation of cyclic keto esters could be achieved. Binaphthyl-derived ammonium catalysts developed by Maruoka and co-workers gave the highest asymmetric induction with up to 79% ee for an indanone-derived keto ester. Throughout this work, asymmetric induction was observed only in the case of benziodoxolone reagents, demonstrating their superiority over conventional alkynyliodonium salts. The deeper understanding gained about the factors leading to higher asymmetric induction will be very useful in the future to develop a truly general and highly enantioselective alkynylation method.

Alkenylureas arising from glycine allylamides were proven to be suitable substrates for the synthesis of bicyclic five-membered ring-fused piperazinones. The reported intramolecular domino processes, performed under oxidative conditions with bis(acetonitrile)palladium dichloride as catalyst and copper(II) chloride in a stoichiometric amount by microwave activation, were completely selective, involving either diamination or aminooxygenation. While the latter process is determined by the direct intervention of the urea oxygen on the σ-alkylpalladium intermediate, the diamination reaction can in principle derive from a direct attack of the second nitrogen atom on the palladium complex or on the first formed chloromethylpiperazinone. Indeed, this latter species was isolated and proved to be capable of conversion solely into the imidazopiperazinone.

The cyclisation of N-allyl-N-substituted-α-polychloroamides is efficiently obtained through a copper-catalysed activators regenerated by electron transfer–atom transfer radical cyclisation process, with a metal load of only 0.5 mol%. The redox catalyst is introduced in its inactive form as copper(II) chloride/[nitrogen ligand] complex, and continuously regenerated to the active copper(I) chloride/[nitrogen ligand] species by ascorbic acid. To preserve the catalyst integrity, the hydrochloric acid, released after each regeneration cycle, has been quenched by carbonate. The choice of the solvent is critical, the best performance being observed in ethyl acetate-ethanol (3:1).