Mechanochemical conditions have been applied to an iridium(III)-catalyzed C−H bond amidation process for the first time. In the absence of solvent, the mechanochemical activation enables the formation of an iridium species that catalyzes the ortho-selective amidation of benzamides with sulfonyl azides as the nitrogen source. As the reaction proceeds in the absence of organic solvents without external heating and yields the desired products in excellent yields within short reaction times, this method constitutes a powerful, fast, and environmentally benign alternative to the common solvent-based standard approaches.

Mechanosynthesis is a valuable technique, offering attractive alternatives for the preparation of organic, inorganic, and organometallic products. Surprisingly, mechanochemical enzymatic transformations have only scarcely been studied until now. Here, we demonstrate the use of lipase B from Candida antarctica (CALB) in acylative kinetic resolutions of secondary alcohols in mixer and planetary mills. Despite the mechanical stress caused by the high-speed ball milling, the biocatalyst proved highly effective, stable, and, in part, recyclable under the applied mechanochemical conditions.

Rhodium-catalyzed ortho-amidations of sulfoximines lead to key intermediates for the preparation of thiadiazine 1-oxides. Following a straightforward protocol, a variety of synthetically valuable compounds can be obtained, thus circumventing common multistep approaches towards potentially bioactive products.

Under an atmosphere of dioxygen, copper-catalyzed de-alkylation/amination sequences provide sulfonimidamides from unprotected sulfoximines in moderate to good yields. Mechanistic studies suggest the involvement of radicals in both the C−S bond cleavage and the formation of the new N−S bond.

A dual C−H/N−H dehydrogenative coupling of quinoline-type N-oxides with sulfoximines that leads to N-(hetero)arylsulfoximines in high yields has been realized by using a catalytic amount of CuBr in air. The method does not require any additional ligand, base, reactivity modifier or oxidant and provides a practical route towards a series of sulfoximidoyl-functionalized quinolines and derivatives.

Mechanochemical conditions have been applied to an iridium(III)-catalyzed C−H bond amidation process for the first time. In the absence of solvent, the mechanochemical activation enables the formation of an iridium species that catalyzes the ortho-selective amidation of benzamides with sulfonyl azides as the nitrogen source. As the reaction proceeds in the absence of organic solvents without external heating and yields the desired products in excellent yields within short reaction times, this method constitutes a powerful, fast, and environmentally benign alternative to the common solvent-based standard approaches.

A one-pot Michael addition/cyclization/condensation reaction sequence for the regioselective synthesis of 1,2-thiazines, starting from propargyl ketones and NH-sulfoximines or NH-sulfondiimines, has been developed. Under mild and operationally simple reaction conditions previously unprecedented 1,2-thiazine 1-imide and 1-oxide derivatives are formed in good to excellent yields. The products represent heterocyclic building blocks, readily modifiable by a regioselective C−H bond functionalization, classical cross-coupling reactions, and deprotection.

Transition-metal-free oxidative iodination of 2-substituted 1,3,4-oxadiazoles was achieved by using sodium iodide as the halide source and Selectfluor as the oxidant. Variously substituted products were obtained in moderate to good yields under operationally straightforward conditions. Compared to existing methods for analogous conversions, the newly developed protocol appears synthetically attractive.

N-Acyl nitrenes have been generated from a range of heterocyclic precursors, and their applications in light-induced ruthenium-catalyzed sulfur imidations have been studied. Analyzing the reaction scope and determining the structural requirements of the in situ formed electrophilic nitrogen species for effective nitrene transfer allowed a mechanistic scheme to be proposed. The mechanistic conclusions were substantiated by the identification of potential intermediates.

As a result of our recent investigations into the N-functionalization of sulfoximines, an iron-catalyzed dealkylative acylation of N-alkylsulfoximines has been developed. This process involves a Polonovski-type dealkylation of an N-alkylated sulfoximine to afford a reactive intermediate that is trapped in the presence of a suitable aldehyde or anhydride to afford N-acyl- and N-aroylsulfoximine derivatives in one pot. Subsequent cleavage of the acyl or aroyl group under acidic conditions generates a synthetically valuable NH-sulfoximine.

The syntheses of a series of enantiopure conformationally restricted benzothiazine and thiazinoquinoline derivatives are presented. Key starting materials are 3-aminoacetophenone and (S)-S-methyl-S-phenylsulfoximine. By using a short reaction sequence, the 8-amino-2,1-benzothiazine derivative was readily prepared, which served as a valuable intermediate for the synthesis of additional derivatives. Initial experiments show that employing such compounds in copper-catalyzed asymmetric Mukaiyama-type aldol reactions provided products with moderate enantioselectivity.

Exposing ortho-amido aroylsilanes to visible light or heat leads to cyclization reactions that provide N-heterocyclic compounds via siloxycarbenes as key intermediates. The previously unreported starting materials have been prepared by directed amidations of aromatic acylsilanes in the presence of an iridium catalyst followed by N-alkylation.

Rhodium-catalyzed directed carbene insertions into aromatic CH bonds of S-aryl sulfoximines lead to intermediates, which upon dehydration provide 1,2-benzothiazines in excellent yields. The domino-type process is regioselective and shows a high functional-group tolerance. It is scalable, and the only by-products are dinitrogen and water. Three illustrative transformations underscore the synthetic value of the products.

In a proof-of-principle study, a planetary ball mill was applied to rhodium(III)-catalyzed CH bond functionalization. Under solventless conditions and in the presence of a minute amount of Cu(OAc)₂, the mechanochemical activation led to the formation of an active rhodium species, thus enabling an oxidative Heck-type cross-coupling reaction with dioxygen as the terminal oxidant. The absence of an organic solvent, the avoidance of a high reaction temperature, the possibility of minimizing the amount of the metallic mediator, and the simplicity of the protocol result in a powerful and environmentally benign alternative to the common solution-based standard protocol.

A new transition metal-free method for the preparation of substituted imidazoles from easy-to-handle amidine hydrochlorides and bromoacetylenes has been developed. The reactions proceed in air and use inexpensive K₂CO₃ as base. Additions of 2,2′-bipyridine and water have beneficial effects on the product yields. Various di- and trisubstituted imidazoles have been prepared in good yields (up to 88 %).

A highly stereoselective vinylogous Mukaiyama Michael reaction (VMMR) leading to α-keto phosphonate-containing γ-butenolides with two stereogenic centers is described. The presented transformation is catalyzed by a combination of a commercially available C₂-symmetric bisoxazoline (BOX) ligand and a copper salt and tolerates a variety of nucleophiles and electrophiles. The stereoselectivities of the reactions are good to excellent and the products are obtained in moderate to high yields.

In the presence of LiBr, a palladium/copper combination catalyzes dehydrogenative amidobrominations of acrylates with NH-sulfoximines, leading to N-vinylated products by dual NH/CH coupling, followed by oxidative enamide bromination. Mechanistically, the domino process is proposed to involve palladium(II) species as key intermediates. First synthetic applications of the products have been demonstrated.

Exposing ortho-amido aroylsilanes to visible light or heat leads to cyclization reactions that provide N-heterocyclic compounds via siloxycarbenes as key intermediates. The previously unreported starting materials have been prepared by directed amidations of aromatic acylsilanes in the presence of an iridium catalyst followed by N-alkylation.

In a proof-of-principle study, a planetary ball mill was applied to rhodium(III)-catalyzed CH bond functionalization. Under solventless conditions and in the presence of a minute amount of Cu(OAc)₂, the mechanochemical activation led to the formation of an active rhodium species, thus enabling an oxidative Heck-type cross-coupling reaction with dioxygen as the terminal oxidant. The absence of an organic solvent, the avoidance of a high reaction temperature, the possibility of minimizing the amount of the metallic mediator, and the simplicity of the protocol result in a powerful and environmentally benign alternative to the common solution-based standard protocol.

Rhodium-catalyzed directed carbene insertions into aromatic CH bonds of S-aryl sulfoximines lead to intermediates, which upon dehydration provide 1,2-benzothiazines in excellent yields. The domino-type process is regioselective and shows a high functional-group tolerance. It is scalable, and the only by-products are dinitrogen and water. Three illustrative transformations underscore the synthetic value of the products.

Acylsilanes are known to undergo a 1,2-silicon-to-oxygen migration under thermal or photochemical conditions to form siloxycarbenes. However, there are few reports regarding the application of siloxycarbenes in organic synthesis and surprisingly, their reaction with CC double or triple bonds remains virtually unexplored. To facilitate such a study, previously inaccessible aromatic acylsilanes containing an ortho-tethered CC double bond were identified as suitable substrates. To access these key intermediates, we developed a new synthetic method utilizing a rhodium-catalyzed oxidative Heck-type olefination involving the application of an acylsilane moiety as a directing group. When exposed to visible-light irradiation, the ortho-olefinated acylsilanes underwent a smooth intramolecular cyclization process to afford valuable indanone derivatives in quantitative yields. This result paves the way for the development of new transformations involving siloxycarbene intermediates.

Acylsilanes are known to undergo a 1,2-silicon-to-oxygen migration under thermal or photochemical conditions to form siloxycarbenes. However, there are few reports regarding the application of siloxycarbenes in organic synthesis and surprisingly, their reaction with CC double or triple bonds remains virtually unexplored. To facilitate such a study, previously inaccessible aromatic acylsilanes containing an ortho-tethered CC double bond were identified as suitable substrates. To access these key intermediates, we developed a new synthetic method utilizing a rhodium-catalyzed oxidative Heck-type olefination involving the application of an acylsilane moiety as a directing group. When exposed to visible-light irradiation, the ortho-olefinated acylsilanes underwent a smooth intramolecular cyclization process to afford valuable indanone derivatives in quantitative yields. This result paves the way for the development of new transformations involving siloxycarbene intermediates.

Rhodium-catalyzed directed CH-functionalizations have been used in hydroarylations of heterobicyclic alkenes with NH-sulfoximines. Unexpectedly, the bicyclic framework is retained, resulting in the formation of addition products being attractive intermediates for functionalized molecules that are difficult to prepare by other means.

Two new rhodium-catalyzed oxidative couplings between sulfoximine derivatives and alkenes by regioselective CH activation, affording ortho-olefinated (Heck-type) products, are reported. A synthetic application of the ortho-alkenylated products into the corresponding cyclic derivatives has been demonstrated, and a mechanistic rational for the rhodium catalysis is presented.

A procedure that enables high yielding access to phosphonic γ-(hydroxyalkyl)butenolides with excellent regio-, diastereo- and enantiocontrol is reported. The simultaneous construction of up to two adjacent quaternary stereogenic centers by a catalytic asymmetric vinylogous Mukaiyama aldol reaction unites biologically and medicinally relevant entities, namely α-hydroxy phosphonates and γ-(hydroxyalkyl)butenolides. This is achieved by utilizing a readily available chiral copper-sulfoximine catalyst showing a broad functional group tolerance for both the electrophilic and nucleophilic reactants. A discussion about potential factors affecting the observed level of enantioselectivity, which stems from the enantiopure sulfoximine ligand, is also included.

Kinetic resolution of racemic sulfoxides requires either custom substrates or shows moderate enantioselectivity, leading to achiral coproducts (such as sulfones) as an intrinsic part of the process. A new strategy is demonstrated that allows the resolution of racemic sulfoxides through catalytic asymmetric nitrene-transfer reactions. This approach gives rise to both optically active sulfoxides and highly enantioenriched sulfoximines. By using a chiral iron catalyst and a readily available iodinane reagent, high selectivity factors have been achieved under very practical reaction conditions. With respect to the substrate scope, it is noteworthy that this unprecedented imidative kinetic resolution of racemic sulfoxides provides access to both aryl–alkyl and dialkyl sulfoximines in highly enantioenriched forms.

1,4,2-Dioxazol-5-ones are five-membered heterocycles known to decarboxylate under thermal or photochemical conditions, thus yielding N-acyl nitrenes. Described herein is a light-induced ruthenium-catalyzed N-acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2-dioxazol-5-ones at room temperature, thus providing direct access to N-acyl sulfimides and sulfoximines under mild reaction conditions. In addition, a one-pot sulfur imidation/oxidation sequence catalyzed by a single ruthenium complex is reported.

1,4,2-Dioxazol-5-ones are five-membered heterocycles known to decarboxylate under thermal or photochemical conditions, thus yielding N-acyl nitrenes. Described herein is a light-induced ruthenium-catalyzed N-acyl nitrene transfer to sulfides and sulfoxides by decarboxylation of 1,4,2-dioxazol-5-ones at room temperature, thus providing direct access to N-acyl sulfimides and sulfoximines under mild reaction conditions. In addition, a one-pot sulfur imidation/oxidation sequence catalyzed by a single ruthenium complex is reported.

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.

An efficient catalytic protocol for the synthesis of δ,δ-bis(aryl)-substituted β-keto esters has been developed. This method involves the Lewis acid catalysed disubstitution reaction of ester-substituted silyl enol ether acetals with a series of aromatic nucleophiles to afford valuable functionalized β-keto esters with several sites available for further derivatisation.

An efficient catalytic system for Sonogashira–Hagihara-type reactions displaying ligand acceleration in the copper-catalyzed formation of C(sp²)C(sp) bonds is described. The structure of the ligand plays a key role for the coupling efficiency. Various copper sources show excellent catalytic activity, even in sub-mol % quantities. A wide variety of substituents is tolerated in the substrates. Mechanistic details have been revealed by kinetic measurements and DFT calculations.

Phosphorylated sulfonimidamides (SIAPhos) undergo ion exchange reactions with cationic complexes, [Rh(cod)₂BF₄] and [Ir(cod)₂BarF], or neutral complexes [Rh(cod)Cl]₂ and [Ir(cod)Cl]₂, leading to unprecedented neutral complexes with P-N-S-N chelates. Use of the resulting neutral iridium complexes in asymmetric hydrogenation reactions of tri- and tetrasubstituted enamides leads to products with high enantioselectivities (up to 92% ee).

The palladium-catalyzed direct CH bond acetoxylation of [2.2]paracyclophanes has been investigated. Various mono- and disubstituted [2.2]paracyclophanes were subjected to typical Sanford acetoxylation conditions. Oxime ethers, an oxime acetate, a pyridine, and a pyrazole with [2.2]paracyclophane cores underwent direct ortho-acetoxylation in good to excellent yields using 1–5 mol% of palladium(II) acetate in combination with iodobenzene diacetate as oxidant. The reactions could be performed on a multigram scale, and the ortho-acetoxylated [2.2]paracyclophanes were suitable for further functionalizations affording a hydroxy[2.2]paracyclophane derivative and a planar chiral benzoxazole.

A general method for the N-arylation of sulfondiimines with aryl bromides using tris(dibenzylideneacetone)dipalladium(0) [Pd₂(dba)₃] and 2-dicyclohexylphosphino-2′,6′-diisopropoxybiphenyl (RuPhos) as catalyst system was developed. A new benzothiazine was obtained, and a protocol for the cleavage of para-methoxyphenyl (PMP) groups in PMP-protected sulfondiimines has been found, which provides access to synthetically useful NH-derivatives, that are difficult to prepare by other means.

Visible light initiates the stereoselective formation of two new bonds, a CC and a CSi bond, during the addition of acylsilanes to alkynes. At room temperature this photochemically induced transformation can be applied for the preparation of chromone derivatives in a highly atom-economic manner.

The successful development of planar-chiral bis-silanols 3a–d and their application as asymmetric organocatalysts in hetero-Diels–Alder (HDA) reactions is described. All precursors were easily prepared by addition of commerically available silyl electrophiles to a dilithiated [2.2]paracyclophane derivative followed by silane oxidations. The analogous bis-carbinols 7a–c have been prepared by addition of suitable Grignard reagents to bis-methoxycarbonyl derivative 6. Both racemic as well as enantiopure planar-chiral bis-silanols and bis-carbinols were obtained in good yields. The catalytic activities of the bis-silanols were analyzed by monitoring HDA reactions between Rawal's diene and aldehydes by in situ IR spectroscopy and comparing the resulting data with those obtained in catalyses with the corresponding bis-carbinol derivatives. The results show for the first time that planar-chiral bis-silanols with hydrogen-bonding capabilities can be applied as asymmetric organocatalysts leading to enantiomerically enriched products.

The synthesis of planar chiral carbazoles bearing a [2.2]paracyclophane backbone is described. Starting from readily available 4-bromo[2.2]paracyclophane planar chiral carbazoles are obtained in a two-step synthesis by Pd-catalyzed CN cross-coupling and subsequent oxidative cyclization.

A gram-scale synthetic access to diastereomerically pure dilignol β-O-4 type model compounds, which represent valuable candidates for studies of lignin cleavage and valorization, is described. Following a straightforward procedure both diastereoisomers of 1,3-dilignols can be prepared. In the key-step, tert-butyl aryloxy esters are used as enolate precursors for additions on aldehydes. After separation, the resulting erythro and threo β-hydroxy esters are independently reduced to afford the target compounds in high yields.

Intramolecular CO bond forming reactions of aryl 2-bromobenzyl ketones lead to benzo[b]furans. The cyclizations can be catalyzed by 10 mol% of iron trichloride (of 98% or of 99.995% purity) or sub-mol% quantities of copper(II) chloride (of 99.995% purity).

Sulfoximines bearing pyrazolylmethyl and aryl substituents, which are relevant to the crop protection industry, and their corresponding sulfilimine intermediates, have been prepared from sulfide precursors by either iron-catalyzed nitrogen transfer reactions or metal-free imination procedures. Whereas the former approach leads to N-nosyl-substituted products, the latter affords N-cyano derivatives.

Potassium hydroxide (KOH) in dimethyl sulfoxide (DMSO) forms a superbasic medium that allows one to access cross-coupling products from reactions between aryl halides with various sulfur-, oxygen- and nitrogen-based nucleophiles under transition metal-free conditions.

N-Heteroarylations of alkyl- and arylamines with various heteroaryl halides have been achieved by ligand-free copper-catalyzed cross-couplings affording aminopyridines and aminopyrimidines in moderate to high yields (up to 99% yield).

Straightforward syntheses of enantiopure N-benzoyl- and N-tert-butyloxycarbonyl-protected sulfonimidamides, which can be used as building blocks in newly designed catalysts, are presented. Key synthetic step is a dynamic resolution of a racemic sulfinic acid sodium salt. All subsequent transformations proceed stereospecifically. The absolute configurations at the sulfur atoms of both sulfonimidamides were determined by comparison of measured and calculated CD spectra. An X-ray crystal structure determination of a sulfonimidoylguanidine derivative confirmed this result.

Vinylogous Mukaiyama-type aldol reactions have been catalyzed by a combination of Cu(OTf)₂ and readily available C₁-symmetric aminosulfoximines. After a fine-tuning of the reaction conditions and an optimization of the modularly assembled ligand structure, high stereoselectivities and excellent yields have been achieved in catalyzed reactions involving various electrophile/nucleophile combinations. The relative and absolute configurations of two products were assigned by X-ray single crystal structure analysis and a comparison of calculated and experimental CD spectra.

The mechanism of the ruthenium-catalyzed dehydrogenation of methanol has been investigated by using three DFT-based methods. Three pathways were considered in which the ruthenium catalyst was ligated by either two or three phosphine ligands. Dispersion interactions, which are not described by the popular B3LYP functional, were taken into account by using the dispersion-corrected B3LYP-D and M06 density functionals. These interactions were found to be important in the description of reaction steps that involved ligand/substrate/product association with or dissociation from the catalyst. In line with experimental results, the resting state of the catalyst was predicted to be a ruthenium trihydride complex. It is shown that the dehydrogenation reaction preferentially proceeds through pathways in which the catalyst is ligated by two phosphine ligands. The catalytic cycle of the dehydrogenation process involves an intermolecular proton transfer from the methanol substrate to the catalyst followed by the release of dihydrogen. Rate-determining β-hydride elimination from the resulting methoxide species then regenerates the resting state of the catalyst and completes the catalytic cycle. The overall free-energy barriers of 29.6–31.4 kcal mol⁻¹ predicted by the three density functionals are in good agreement with the experimentally observed reaction rate of 6 h⁻¹ at 423 K.

A C₁-symmetric amino sulfoximine has been used as a chiral ligand in copper-catalyzed asymmetric halogenation reactions of β-oxo esters. Both the catalyst itself and the reaction conditions were optimized, and 26 fluorinated, chlorinated, and brominated products were obtained with enantioselectivities of up to 91 % ee in yields of up to 99 %. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

A series of naphthalene-bridged P,N-type sulfoximine ligands and their iridium complexes have been synthesized. They were applied in the enantioselective hydrogenation of quinoline derivatives, and enantioselectivities up to 92% ee have been achieved in the hydrogenation of 2-methylquinoline.

A small quantity of iron(II) triflate (2.5 to 5 mol%) catalyzes the aziridination reactions of enol silyl ethers with tosylimino(iodo)benzene (PhINTs) in acetonitrile to give α-N-tosylamido ketones by subsequent aziridine ring opening. Olefins are converted into aziridines by 5 mol% of this catalyst system. Both reactions afford the corresponding products in moderate to good yields. In the presence of chiral ligands asymmetric aziridinations have been achieved.

An inexpensive and experimentally simple, iron-catalyzed N-arylation reaction of NH-sulfoximines with aryl iodides is reported. This complementary method to the known palladium- and copper-catalyzed ones features the use of a combination of environmentally friendly FeCl₃ and N,N′-dimethylethylenediamine (DMEDA) as catalytic system and allows the efficient preparation of various N-arylsulfoximines in high yields.