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A combined computational and experimental approach allowed us to develop overall the most selective catalyst for the direct hydrogenation of N‐methyl, N‐alkyl and N‐aryl imines described to date. Iridium catalysts with a cyclometallated cyclic imide group provide selectivity of up to 99 % enantiomeric excess. Computational studies show that the selectivity results from the combined effect of H‐bonding of the imide C=O with the substrate iminium ion and a stabilizing π–π interaction with the cyclometallated ligand. The cyclometallated ligand thus exhibits a unique mode of action, serving as a template for the H‐bond directed approach of the substrate which results in enhanced selectivity. The catalyst (2) has been synthesized and isolated as a crystalline air‐stable solid. X‐ray analysis of 2 confirmed the structure of the catalyst and the correct position of the imide C=O groups to engage in an H‐bond with the substrate. 19F NMR real‐time monitoring showed the hydrogenation of N‐methyl imines catalyzed by 2 is very fast, with a TOF of approx. 3500 h−1. [ABSTRACT FROM AUTHOR]

A one‐pot Pd‐catalyzed tandem process to prepare (2‐arylallyl) aryl sulfones has been developed. This strategy is based on the modular assembly of a boronic acid, a sodium sulfinate and 2‐bromoallyl acetate. The reaction is completely regioselective towards the terminal alkene, yielding (2‐arylallyl) aryl (or alkyl) sulfones with yields ranging from 56 to 93%. Control experiments together with DFT calculations allowed to propose a plausible reaction mechanism of the tandem reaction. The usefulness of this methodology has been demonstrated with the formal synthesis of the marketed drug Apremilast and of several natural products by asymmetric hydrogenation. Using the commercially available UbaPHOX iridium complex, chiral β‐methyl sulfones with up to 98% ee were obtained [ABSTRACT FROM AUTHOR]

This study details an aluminum‐catalyzed regioselective isomerization of 2,2‐disubstituted oxetanes to yield homoallylic alcohols. The reaction takes place in toluene at 40 °C, employing 1 mol % of Al(C6F5)3 as catalyst. This catalytic system shows a wide substrate scope (12 examples). The optimized conditions are especially useful for electron‐rich aryl oxetanes, completely suppressing the formation of allyl isomers and reducing the amount of the dimer by‐product. The synthetic applicability of the reported methodology is demonstrated by the enantioselective formal synthesis of curcuquinone and the σ1 receptor agonist RC‐33. [ABSTRACT FROM AUTHOR]

Simple Summary: The compounds named PROTACs are formed by two fragments, which bring together a particular protein with a ubiquitinating enzyme. This allows ubiquitination and degradation of the targeted protein. Ubiquitination-mediated protein degradation is an important regulatory process to control the expression levels of proteins and maintain the homeostatic conditions in cells. Thus, by re-directing a mechanism that is normally used for cell regulation, PROTACs allow to remove specific proteins associated to particular diseases or pathological conditions. In this paper, we report a type of PROTAC that targets for degradation the protein named p38α, whose functions have been linked to cancer and other diseases. We show that these PROTACs effectively reduce p38α protein expression not only in several cancer cell lines but also in tumors generated in mice. These compounds may provide an attractive strategy to evaluate potential therapeutic applications for targeting p38α in the clinical context. We report a series of small molecule proteolysis-targeting chimeras (PROTACs) that target the protein kinase p38α for degradation. These PROTACs are based on a ligand of the VHL E3 ubiquitin ligase, which is linked to an ATP competitive inhibitor of p38α. We provide evidence that these compounds can induce the specific degradation of p38α, but not p38β and other related kinases, at nanomolar concentrations in several mammalian cell lines. We also show that the p38α-specific PROTACs are soluble in aqueous solutions and therefore suitable for their administration to mice. Systemic administration of the PROTACs induces p38α degradation only in the liver, probably due to the PROTAC becoming inactivated in that organ, but upon local administration the PROTACs induce p38α degradation in mammary tumors. Our compounds provide an alternative to traditional chemical inhibitors for targeting p38α signaling in cultured cells and in vivo. [ABSTRACT FROM AUTHOR]

Synthesis and use of Pulegone-derived bidentate P,S ligands PuPHOS and CyPuPHOS in the intermolecular Pauson-Khand reaction (PKR) were described. Intermolecular PKR of trimethylsilylacetylene complex occurred in a completely stereospecific fashion to yield optically enriched cyclopentenone.

Chiral compounds containing nitrogen heteroatoms are fundamental substances for the chemical, pharmaceutical and agrochemical industries. However, the preparation of some of these interesting scaffolds is still underdeveloped. Herein we present the synthesis of a family of P‐stereogenic phosphinooxazoline iridium catalysts from L‐threonine methyl ester and their use in the asymmetric hydrogenation of N‐Boc‐2,3‐diarylallyl amines, achieving very high enantioselectivity. Furthermore, the synthetic utility of the 2,3‐diarylpropyl amines obtained is demonstrated by their transformation to 3‐aryl‐tetrahydroquinolines and 4‐benzyl‐tetrahydroisoquinolines, which have not yet been obtained in an enantioselective manner by direct reduction of the corresponding aromatic heterocycles. This strategy allows the preparation of these types of alkaloids with the highest enantioselectivity reported up to date. [ABSTRACT FROM AUTHOR]

A simple and convenient methodology for the preparation of optically pure 2-amino-2-aryl-1,1-diphenylethanols is presented. Removal of allyl protecting group provided the free 1,2-amino alcohols in enantiomerically pure form.

1,2,4,5-Tetrazines have become extremely useful tools in chemical biology. However, the synthesis of some challenging substrates such as asymmetrically disubstituted alkyltetrazines is still a limitation for the widespread use of this class of compounds. Herein we describe an efficient route to these compounds based on the Sonogashira coupling of 3-bromo-6-methyl-1,2,4,5-tetrazine and 3-bromo-6-phenyl-1,2,4,5-tetrazine with terminal alkynes. The preparation of the starting reagents has also been optimized. The alkynyl products have been used as intermediates for the synthesis of dialkyl-tetrazines through a sequence of hydrogenation and re-oxidation with unprecedented yields. The synthetic applicability of this new approach is showcased through the preparation of several unnatural amino acids bearing alkynyl- and alkyl-1,2,4,5-tetrazine fragments. [ABSTRACT FROM AUTHOR]

The asymmetric isomerization of primary allylic alcohols to chiral aldehydes using iridium‐catalysts bearing P,N‐MaxPHOX ligands has been studied. These catalysts can be fine‐tuned as they present three different stereogenic centers to modulate both the reactivity and enantioselectivity of a family of different substrates. The experimental part is supported by a DFT study of the reaction mechanism, which provides new insights into the key steps of this transformation. [ABSTRACT FROM AUTHOR]

The selective isomerization of strained heterocyclic compounds is an important tool in organic synthesis. An unprecedented regioselective isomerization of 2,2‐disubstituted oxetanes into homoallylic alcohols is described. The use of tris(pentafluorophenyl)borane (B(C6F5)3), a commercially available Lewis acid was key to obtaining good yields and selectivities since other Lewis acids afforded mixtures of isomers and substantial polymerization. The reaction took place under exceptionally mild reaction conditions and very low catalyst loading (0.5 mol %). DFT calculations disclose the mechanistic features of the isomerization and account for the high selectivity displayed by the B(C6F5)3 catalyst. The synthetic applicability of the new reaction is demonstrated by the preparation of γ‐chiral alcohols using iridium‐catalyzed asymmetric hydrogenation. [ABSTRACT FROM AUTHOR]

A myriad of tricyclo[5.2.1.0]deca-4,8-dien-3-ones is prepared by using norbornadiene as alkene. The interpretation of the experiments is that the photorearrangement has taken place through [super 3]([pi][pi]*) state as the energy barrier involved in the initial C-C [gamma]-bond cleavage of the enone is much lower in the [super 3]([pi][pi]*) potential energy surface (PES) than in the [super 1](n[pi]*) PES.

The synthesis of a family of racemic and optically pure N-phosphino-p-tolylsulfinamide (PNSO) ligands and their stability and coordination behavior toward dicobalt-alkyne complexes are reported. The results provide insight into the presence of an aryl group on the sulfinamide that reduces the hemilabile character of the PNSO ligands.

A unique methine moiety attached to three heteraoatoms (O,P,S) and contained in the PuPHOS and CamPHOS ligands serves as a strong hydrogen-bond donor. The hydrogen-bond bias obtained in the ligand exchange process is exploited in the asymmetric intermolecular Pauson-Khand reaction to yield the corresponding cyclization adducts.

The introduction of 2-piperidino-1,1,2-triphenylethanol as a catalyst, has led to the ligand-catalyzed arylation of aldehydes. The kinetic, experimental and theoretical reports describe the different aspects involved in the most synthetically useful phenylation reaction.

The iridium‐catalyzed asymmetric hydrogenation of several N‐sulfonyl allyl amines is reported. All substrates can be easily obtained by the Ir‐catalyzed isomerization of N‐tosylaziridines reported previously. The commercially available threonine‐derived phosphinite (UbaPHOX) iridium complex has been found to be the best catalyst for this catalytic application, affording β‐methyl amines with good to excellent ee values (up to 94%). The synthetic potential of this novel methodology was demonstrated by the formal synthesis of Lorcaserin and LY‐404187. [ABSTRACT FROM AUTHOR]

The isomerization of epoxides to aldehydes using the readily available Crabtree's reagent is described. The aldehydes were transformed into synthetically useful amines by a one‐pot reductive amination using pyrrolidine as imine‐formation catalyst. The reactions worked with low catalyst loadings in very mild conditions. The procedure is operationally simple and tolerates a wide range of functional groups. A DFT study of its mechanism is presented showing that the isomerization takes place via an iridium hydride mechanism with a low energy barrier, in agreement with the mild reaction conditions. [ABSTRACT FROM AUTHOR]

The use of ethylene glycol (15% v/v in toluene) as additive in the catalytic Pauson-Khand reaction (PKR) is reported. In most cases both the yield and selectivity were enhanced compared to standard protocols. Moreover, the immiscibility of ethylene glycol in toluene allowed recycling of the catalyst (which remained mainly in the ethylene glycol). The recycling allowed catalyst loading to be reduced to only 3 mol%. A gram-scale reaction was also performed, allowing the use of only 1 mol% of Co2(CO)8, the lowest amount reported so far in intermolecular cobalt-catalyzed PKR. [ABSTRACT FROM AUTHOR]

Both enantiomers of the optically pure Secondary Phosphine Oxide (SPO) t-BuMeP(O)H (1) have been obtained by deboronation of phosphinous acid-borane t-BuMeP(O)H·BH3 (3) with HBF4 followed by hydrolysis of the intermediate adduct t-BuMeP(O)H·BF3 (1·BF3), which has been isolated and crystallographically characterised. Complexes [MCl(COD)(κP-(R)-1)] (M = Ir, Rh; 4 and 7 respectively) have been detected in solution but could not be isolated while trans-[RhCl(CO)(κP-(S)-1)2] (9) has been successfully obtained in good yield. Gold complex [AuCl(κP-(S)-1)] (10) has been prepared and its crystal structure shows the presence of aurophilic interactions. Three new ruthenium complexes ([RuCl2(η6-p-cymene)(κP-(R)-1)], 12), ([RuCl2(CO)3(κO-(S)-1)], 13) and trans-([RuCl2(CO)2(κP-(S)-1)2], 14) have been synthesised and fully characterised, including the crystal structure of 12. Four palladium coordination compounds have been prepared: trans-[PdCl2(κP-(S)-1)2] (trans-15), [Pd(μ-Cl)(κP-(S)-1)2]2 (16·OH and 16·BF2) and [Pd(μ-OAc)(κP-(S)-1)2] (17) and the crystal structure of complex 16·OH proves the pseudobidentate coordination of the two molecules of 1. Three organometallic allylpalladium complexes have been prepared namely [Pd(η3-Ph2C2H3)Cl(κP-(S)-1)] (18) and [Pd(η3-Ph2C2H3)(κP-(S)-1)2] (19·OH and 19·BF2). The crystal structure of 19·BF2 constitutes the first allylpalladium-SPO complex reported to date. [ABSTRACT FROM AUTHOR]

A stereoselective synthesis of 2-acetamido-1,2-dideoxyaltronojirimycin (8) and its manno epimer 9 is described. The synthetic approach is based on key bicyclic carbamate 7, which is easily accessible with high enantiomeric purity on a multigram scale by Sharpless asymmetric epoxidation of 1,4-pentadien-3-ol or 2,4-pentadien-1-ol. This procedure completes an efficient stereodivergent approach to five isomers of 2-acetamido-1,2-dideoxyiminosugars in high overall yields starting from the same key intermediate 7. The approach described in this paper is based on control of the stereoselectivity of the sulfite ring-opening reaction to give retention of configuration through anchimeric assistance from the endocyclic amine. [ABSTRACT FROM AUTHOR]

The reaction of the acetylacetonates [(η5-C5Me5)M(acac)Cl] with (SP)-[HMaxPhos][BF4] afforded cationic complexes with the formula (SM,RP)-[(η5-C5Me5)MCl(MaxPhos)][BF4] (M = Rh (1), Ir (2)). The reaction of (SP)-MaxPhos with [RuCl(μ-Cl)(η6-p-MeC6H4iPr)]2 and NH4X afforded (SRu,RP)-[(η6-p-MeC6H4iPr)RuCl(MaxPhos)][X] (X = BF4 (3), PF6 (3′)). The complexes have been completely characterized by analytical and spectroscopic means, including the determination of the crystal structures of 1, 2 and 3′. Treatment of the iridium complex 2 with AgBF4, at 253 K, resulted in the intramolecular cyclometallation of one of the tert-butyl substituents of the MaxPhos diphosphane ligand, affording a mixture of isomers of (SIr,RP1,SP2 and RIr,RP1,RP2)-[(η5-C5Me5)Ir(MaxPhos)][BF4] (4a and 4b). However, rhodium complex 1 and ruthenium complex 3 reacted with AgBF4 forming the expected unsaturated intermediates “(ηn-ring)M(MaxPhos)” which were trapped by MeCN, affording the cationic adducts (SM,RP)-[(ηn-ring)M(MaxPhos)(MeCN)][BF4]2 (M = Rh (5), Ru (6)). Only one epimer at the metal was isolated in high yield for the complexes 1, 2, 3, 3′, 5 and 6 and the metallation of 2 to give 4 occurs with high diastereoselectivity. [ABSTRACT FROM AUTHOR]

The use of ethylene glycol as additive in the N-oxide-promoted intermolecular Pauson-Khand reaction (PKR) has been studied. The addition of 15% ethylene glycol to the reaction mixture consistently increased (from 20% up to 2-4-fold) the reaction yields. [ABSTRACT FROM AUTHOR]

The nickel(0)-catalyzed carbonylative cycloaddition of 1,5- and 1,6-ene-imines with carbon monoxide (CO) is reported. Key to this reaction is the efficient regeneration of the catalytically active nickel(0) species from nickel carbonyl complexes such as [Ni(CO)3L]. A variety of tri- and tetracyclic γ-lactams were thus prepared in excellent yields with 100 % atom efficiency. Preliminary results on asymmetric derivatives promise potential in the synthesis of enantioenriched polycyclic γ-lactams. [ABSTRACT FROM AUTHOR]

The synthesis of P-stereogenic bisphosphine ligands starting from a phosphinous acid chiral synthon and hydrazine is reported. The dialkylation of the hydrazine backbone yielded atropo- and nitrogen inversion isomers which are in slow exchange. The crystallization of one of the isomers allowed us to study the reaction kinetics of the equilibria. The new ligands were tested in the Rh catalysed asymmetric hydrogenation of various benchmark substrates attaining up to 99% ee. [ABSTRACT FROM AUTHOR]