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An o-quinone methide (o-QM) featuring an overcrowded olefinic framework is introduced, which exhibits dehydridation activity owing to its enhanced zwitterionic character, particularly through photoexcitation. The characteristics of this o-QM enable the operation of dehydridative catalysis in the oxidation of benzylic secondary alcohols under aerobic photoirradiation conditions. An experimental analysis and density functional theory calculations provide mechanistic insights; the ground-state zwitterionic intermediate abstracts a hydride and proton simultaneously, and the active oxygen species facilitate catalyst regeneration., An o-quinone methide (o-QM) featuring an overcrowded olefinic framework is introduced, which exhibits dehydridation activity owing to its enhanced zwitterionic character, particularly through photoexcitation.

The photocatalytically active salt of a cationic iridium polypyridyl complex and a chiral borate is competent to promote a highly stereoselective [3 + 2]-cycloaddition of cyclopropylurea with α-substituted acrylates. This protocol provides straightforward access to a variety of stereochemically defined 5-membered alicyclic α-quaternary β-amino acids, useful building blocks of β-peptides and peptidomimetics.

The development of a photoinduced, highly diastereo- and enantioselective [3 + 2]-cycloaddition of N-cyclopropylurea with α-alkylstyrenes is reported. This asymmetric radical cycloaddition relies o...

A diastereoselective borylcyclopropanation of α-MIDA-boryl styrenes with 1,1-diiodoborylmethane is developed using 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) as a catalyst under visible-light irradiation. The scope of this photocatalytic method is explored, and the utility of the resulting doubly borylated cyclopropanes is demonstrated by the selective transformation of one of the two boryl groups.

A step toward control of a noxious weed The parasitic plant Striga hermonthica causes extensive crop losses, particularly in Africa. Strigolactone hormones can be used to initiate germination of Striga seeds when no host crop is present, which causes the nascent Striga plants to die. Unfortunately, strigolactones are also used by crop plants to establish beneficial mutualisms. Uraguchi et al. developed a hybrid molecule that can initiate Striga germination without interfering with strigolactone-dependent events in the host (see the Perspective by Bouwmeester). The compound has the potential to diversify routes toward protecting fields from Striga infestation. Science , this issue p. 1301 ; see also p. 1248

The photocatalytically active salt of a cationic iridium polypyridyl complex and a chiral borate is competent to promote a highly stereoselective [3 + 2]-cycloaddition of cyclopropylurea with α-substituted acrylates. This protocol provides straightforward access to a variety of stereochemically defined 5-membered alicyclic α-quaternary β-amino acids, useful building blocks of β-peptides and peptidomimetics.

A divergent photocatalytic system for the reaction of α-bromo nitroalkanes with styrene derivatives is established, wherein the generation of the persistent nitroxyl radical as a junctional intermediate and suitable tuning of the redox ability of the system constitute the crucial elements for achieving rigorous control over the possible reaction pathways.

Catalysis by chiral weakly-coordinating anions (WCAs) remains underdeveloped due to the lack of a molecular design strategy for exploiting their characteristics, such as the non-nucleophilic nature. Here, we report the development of a chiral borate ion comprising an O,N,N,O-tetradentate backbone, which ensures hitherto unattainable structural robustness. Upon pairing with a proton, the hydrogen borate acts as an effective catalyst for the asymmetric Prins-type cyclization of vinyl ethers, providing access to structurally and stereochemically defined dihydropyrans. The key to selectivity control is the distinct ability of the borate ion to discriminate the prochiral faces of the acyclic oxonium ion intermediate and dictate the regiochemical outcome. We anticipate that this study paves the way for exploring the untapped potential of WCA catalysis for selective chemical synthesis.

A highly stereoselective Michael addition of α-amino acid-derived 2-benzyloxythiazol-5(4H)-ones to dimethyl allenedicarboxylate was developed by employing P-spiro chiral triaminoiminophosphorane bearing (S)-sec-butyl groups as a catalyst. Theoretical investigation of the transition-state models for the reaction and control experiments suggested the intervention of a dynamic kinetic resolution of the axially chiral allene acceptor. The synthetic utility of this method was demonstrated through the transformation of the stereochemically homogeneous Michael adduct to an α-vinylic α-amino acid derivative.

A site-divergent stereoselective Michael reaction system is developed based on the identification of two distinct catalysts. Cinchonidine-derived thiourea catalyzes the 1,4-addition of prochiral azlactone enolates to enynyl N-acyl pyrazoles in a highly diastereo- and enantioselective manner to give stereochemically defined alkynes, while P-spiro chiral triaminoiminophosphorane catalytically controls the stereoselective 1,6-addition and the consecutive γ-protonation of the vinylogous enolate intermediate to afford Z,E-configured conjugated dienes. This 1,6-adduct serves as a valuable precursor for the synthesis of a 2-amino-2-deoxy sugar.

A highly chemo-, regio-, and stereoselective glycolate aldol reaction of sulfur-substituted enediolates with aldehydes was developed by employing a l-cyclohexylglycine-derived chiral iminophosphorane as a catalyst. The key for establishing this protocol is the distinct ability of the iminophosphorane catalyst to precisely direct the equilibrium mixture of the enediolates toward the intermolecular carbon-carbon bond formation with simultaneous yet rigorous control of relative and absolute stereochemistry. The critical importance of the cyclohexyl substituents on the catalyst backbone in dictating the reaction pathway and the stereochemical outcome was elucidated through an extensive quantum analysis by density functional theory calculations.

We describe the design, synthesis, and characterization of a chiral hexacoordinated phosphate ion that features an octahedral P(V) core consisting of two N,N,O-tridentate backbones. We further demonstrate that the corresponding hydrogen phosphate acts as an effective catalyst for a highly enantioselective Pictet-Spengler-type reaction, wherein the relationship between the structure of the chiral phosphate ion and its ability to dictate the absolute stereochemistry is revealed in conjunction with precise structural elucidation of the phosphate ion.

A readily available thioxanthone derivative, 3,6-dimethoxy-9H-thioxanthen-9-one, has been utilized as an effective catalyst for the conjugate radical addition of 1,3-dioxolane to α,β-unsaturated ca...

An o-quinone methide (o-QM) competent as a catalyst for the dehydridative oxidation of benzylic alcohols was developed. The introduction of an overcrowded olefinic component into the o-QM induced structural distortion, beneficial for imparting triarylmethylium character and regenerability. The zwitterionc resonance form of the o-QM, generated via photoexcitation and subsequent relaxation, exerted the dehydridation activity. Density functional theory calculations were conducted to gain insights into the operative catalytic process.

Development of highly efficient and enantioselective hydrophosphonylations of aldehydes and ynones mediated by [5.5]-P-spirocyclic chiral triaminoiminophosphoranes as base catalysts is described. T...

An intramolecular ion-pairing acridinium phenoxide possessing a redox-active component and a basic site within a single molecular framework is developed. The potential of the acridinium betaine as a chemical redox catalyst is demonstrated by its application to the homodimerization of 3-aryl oxindoles, which proceeds through proton-coupled electron-transfer pathway. Analysis of the kinetic profile has provided important clues to understand the reaction mechanism.

A novel class of chiral N-sulfonyl oxaziridines is introduced for use as structurally modifiable chiral oxidants. These oxaziridines are readily prepared from N-sulfonyl α-imino esters in a highly enantioenriched form by oxidation with hydrogen peroxide using l-isoleucine-derived triaminoiminophosphorane as a catalyst. The distinct advantage of their structural modularity is demonstrated through the identification of an optimal oxaziridine that exhibits high reactivity and enantiospecificity in the asymmetric oxidation of a silyl enol ether and N-sulfonyl allylic and homoallylic amines.

Unlike carbonyl compounds, it has long been common understanding that excited imines show virtually no photoreactivity, and hence their properties and potential utility in chemical science remain largely unexplored. Now, a strategy is presented for eliciting latent photoreactivity of imines based on the introduction of a donor-acceptor (D-A) structure to extend the lifetime of their photoexcited states. A series of spectroscopic analyses and density functional theory calculations reveal unique photophysical properties of the D-A-type imines. Furthermore, the reactivity of the D-A-type imines is demonstrated by using them as a photoredox catalyst for atom-transfer radical addition. These findings illuminate a previously neglected chemical space in the field of photochemistry, which will be exploited by taking advantage of the inherent structural modularity of imines.

The trifluoromethylation of enamines of ethyl 3-oxocarboxylates catalyzed by Fenton reagent with CF3I was investigated. Trifluoromethylation followed by acid hydrolysis provided 3-oxo-2-(trifluoromethyl)carboxylates in 64–94% yields, which were greater than those obtained by the trifluoromethylation of 3-oxocarboxylates as reported previously. Enamines trifluoromethylated at the 2-position were isolated as intermediates. Hydrolysis and successive decarboxylation of the obtained 3-oxo-2-(trifluoromethyl)carboxylates under acidic conditions provided (2,2,2-trifluoroethyl)ketones in satisfactory yields.

A redox neutral, highly enantioselective coupling between N-arylaminomethanes and N-sulfonyl aldimines was developed by harnessing the efficient catalysis of P-spiro chiral arylaminophosphonium barfate and a transition-metal photosensitizer under visible light irradiation. This mode of synergistic catalysis provides a powerful strategy for controlling the bond-forming processes of reactive radical intermediates.

A highly regio-, diastereo-, and enantioselective 1,6-addition of azlactone to various alkenyl dienyl ketones has been achieved under P-spiro chiral triaminoiminophosphorane catalysis. This site-selectivity control relies on the distinct ability of the conjugate acids of iminophosphoranes, aminophosphonium ions, to precisely differentiate between the three electrophilic reaction sites of alkenyl dienyl ketones, which is further demonstrated by the discriminative asymmetric 1,6-addition of azlactone to dienyl ketones, leaving the coexisting alkenyl ketone intact.

The asymmetric Payne oxidation of N-sulfonyl imines catalyzed by a P-spiro chiral triaminoiminophosphorane was developed for the practical synthesis of optically active N-sulfonyl oxaziridines. High efficiency and an excellent level of enantioselectivity were generally achieved with a wide variety of aldimines by choosing appropriate reaction conditions. The versatility of this method was demonstrated by the diastereoselective kinetic oxidation of racemic α-chiral N-sulfonyl imines.

The studies on the development of a highly enantioselective oxidation of N -sulfonyl imines with hydrogen peroxide–trichloroacetonitrile system utilizing P -spiro chiral triaminoiminophosphoranes as an organic base catalyst are detailed. This method is general and scalable, and exhibits unique chemoselectivity, providing a practical stereoselective route to structurally diverse N -sulfonyl oxaziridines. The mechanistic investigations reveal that the reaction proceeds through the Payne-type oxidation pathway. The synthetic utility of the optically active N -sulfonyl oxaziridines as versatile organic oxidants and chiral building blocks is also demonstrated.

Chiral P-spiro triaminoiminophosphorane (1) was developed to promote the highly regio-, diastereo-, and enantioselective 1,6- and 1,8-additions of azlactones (2·H) to dienyl and trienyl N-acylpyrroles (3 and 4). DFT calculations enabled us to gain deep insight into the whole reaction mechanism as well as the origin of the high regio- and stereoselectivities. The present reaction consists of three steps: (1) formation of the phosphonium-enolate ion-pair complex by deprotonation of 2·H with 1, (2) C–C bond formation of 2 with 3 and 4, and (3) protonation of the resulting enolate anion. The C–C bond formation is irreversible, and the rate- and stereodetermining step. The Cα-protonation preferentially proceeds rather than the thermodynamically and kinetically disfavored O- and Cγ-protonation, respectively. The high regio- and enantioselectivities are mainly attributed to the steric and electronic features of 1·H and 3/4. The hydrogen bonds (NH–O and CH–O) and the attractive CH−π interaction between 1·H and 2 ...

The vinylogous reactivity of α,β-disubstituted nitroolefins was uncovered through the facile generation of the corresponding α-substituted vinylogous nitronates and their use in the development of a highly diastereo- and enantioselective aza-Henry reaction with N-Boc aldimines under the catalysis of chiral ammonium betaines. The novel vinylogous nitronates undergo stereoselective bond formation at the sterically encumbered α-position exclusively, allowing the construction of contiguous tertiary-quaternary stereogenic carbon centers.

Catalytic systems that allow selective generation of any diastereomer of a reaction product bearing multiple stereocentres through minimal modification of a single catalyst scaffold remain elusive, particularly for carbon–carbon bond formations requiring simultaneous control of multiple selectivity factors. Here, we report a catalyst-directed pinpoint inversion of diastereochemical preference in the 1,6-addition of azlactones to δ-aryl dienyl carbonyl compounds with full control over other selectivities preserved. This rigorous diastereodivergence is enabled by the slight structural adjustment of a chiral iminophosphorane catalyst, providing access to all the stereoisomers with high regio-, distereo- and enantioselectivity. The utility of this method is demonstrated in the facile stereodivergent preparation of densely functionalized proline derivatives. The experimental and computational elucidation of the origin of the diastereodivergence is also reported., For reactions producing numerous chiral centres, accessing all potential stereoisomers is synthetically appealing but difficult. Here, the authors report a stereodivergent 1,6-addition of azlactones where minimal changes to the catalyst structure switches the product selectivity.

A catalytic cycle initiated by the oxidative quenching of the excited photosensitizer (Ir*(ppy)3) is established for the enantioselective coupling between (N-arylamino)methanes and (N-methanesulfonyl)aldimines catalyzed by Ir-based photosensitizer and a chiral (arylamino)phosphonium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate under visible light irradiation. This achievement clearly demonstrates the insensitivity of this redox-neutral asymmetric reaction to the sequence of the key redox events involved in the synergistic catalysis.

The trifluoromethylation of enamines of ethyl 3-oxocarboxylates catalyzed by Fenton reagent with CF3I was investigated. Trifluoromethylation followed by acid hydrolysis provided 3-oxo-2-(trifluoromethyl)carboxylates in 64–94% yields, which were greater than those obtained by the trifluoromethylation of 3-oxocarboxylates as reported previously. Enamines trifluoromethylated at the 2-position were isolated as intermediates. Hydrolysis and successive decarboxylation of the obtained 3-oxo-2-(trifluoromethyl)carboxylates under acidic conditions provided (2,2,2-trifluoroethyl)ketones in satisfactory yields.

A new highly stereoselective and metal-free multicomponent coupling reaction between isatins and aldehydes with dialkyl phosphite as an economical reductant is reported.

The ammonium-betain catalyzed aza Henry reaction of in situ generated chiral vinylogous nitronates with N-Boc imines is reported.

Catalytic direct aldol addition of α-hydroxy trialkyl phosphonacetates to aldehydes affords α-hydroxy-β-phosphonyloxy ester products. The fully substituted glycolate enolate intermediate is generated in situ under mild conditions via [1,2]-phosphonate-phosphate rearrangement. High enantioselectivity and dramatic enhancement of reaction diastereocontrol is realized via the application of chiral iminophosphorane catalysts. The phosphate products undergo stereoselective nucleophilic displacement reactions.

Direct trifluoromethylation of 1,3-dicarbonyl compounds with CF3I in the presence of a Fenton reagent in dimethylsulfoxide was investigated. 1,3-Diketones, 3-oxocarboxylates and 3-oxocarboxamides were readily trifluoromethylated at the methylene carbon between two oxo groups. Cycloaddition of hydrazine derivatives to the obtained 2-(trifluoromethyl)-1,3-dicarbonyl compounds provided fluorinated pyrazoles. 4-(Trifluoromethyl)pyrazole derivatives were formed from 2-(trifluoromethyl)-1,3-diketones, while 3-oxo-2-(trifluoromethyl)carboxylates or carboxamides gave 5-fluoropyrazole-4-carboxylates or carboxamides, respectively, via 3-hydrazono-2-(trifluoromethyl)carboxylates or carboxamides as an intermediate.

Highly enantioselective conjugate addition of 2-unsubstituted azlactone 3 to various nitroolefins 4 was accomplished by the selective utilization of supramolecularly assembled, chiral tetraaminophosphonium aryloxide–arylhydroxide 1a·[2a]2 as a requisite catalyst. The key to this achievement is the polarity dependence of the molecular associations of type 1·[2]n and the crucial role of the proximal arylhydroxide 2 as a proton donor. The present method offers an attractive route to various optically active amino carbonyl compounds including β2-amino acids.

A highly stereoselective aza-Henry reaction of α-aryl nitromethanes with aromatic N-Boc imines was established by using C1 -symmetric chiral ammonium betaine as a bifunctional organic base catalyst. Various substituted aryl groups for both imines and nitromethanes were tolerated in the reaction, and a series of precursors for the synthesis of unsymmetrical anti-1,2-diaryl ethylenediamines was provided.

Trifluoromethylation of aromatic and hetero-aromatic compounds by CF3I in the presence of Fe(II) compound, H2O2 and dimethylsulfoxide was investigated. Various trifluoromethylated benzene derivatives, six-membered nitrogen-containing aromatic compounds and five-membered hetero-aromatic compounds were obtained under mild conditions. General orientation of electrophilic substitution of aromatic compounds was observed similarly as reported in other radical trifluoromethylation previously.

A series of P-spiro chiral tetraaminophosphonium salts have been designed and synthesized as a new class of organic molecular catalysts, and their inherent abilities to exert four different, synthetically relevant asymmetric catalyses have been brought out through the unique molecular design on a single core structure, N4P+. Further, these catalyses have been applied to the development of various C-C, C-P, and C-N bond-forming reactions, in which the remarkably high catalytic performances and stereocontrolling abilities of the chiral tetraaminophosphonium salts have been successfully demonstrated.

Catalytic Assembly Most asymmetric catalysts employed in organic chemistry are assembled through binding of chiral ligands to one or more metal ions. Uraguchi et al. (p. 120 , published online 27 August) show that a highly selective catalyst can assemble through hydrogen bonding from a small collection of small molecules in the absence of metals. In the solid state, the catalyst comprises a central chiral phosphonium cation bound to two phenol molecules, which in turn bind a charge-compensating phenoxide ion. In solution, an oxazolone derivative appears to be able to bind in place of the phenoxide, spurring its stereoselective addition to a broad range of esters.

The Ni-catalyzed cross-coupling of 2-bromo-3,3,3-trifluoropropene and aryl Grignard reagents was investigated. When NiCl 2 (PPh 3 ) 2 was used as a catalyst, the highest yield of α-trifluoromethylstyrene (89%) from 2-bromo-3,3,3-trifluoropropene and PhMgBr was obtained in 1,3-dimethyl-2-imidazolidinone at 50 °C for 30 min. Various α-trifluoromethylstyrene derivatives could be produced in satisfactory yields by NiCl 2 (PPh 3 ) 2 -catalyzed coupling using aryl Grignard reagents.