Carboranylphosphites—new effective ligands for rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate

Novel monodentate phosphites containing ortho- and meta-closo-dodecarboranyl groups have been synthesized and applied in the asymmetric Rh-catalyzed hydrogenation of dimethyl itaconate, providing excellent enantioselectivities (up to 99.8% ee in CH₂Cl₂ and up to 93% ee in supercritical CO₂).     

Thermodynamic analysis of the ionization of ortho and para toluic acids : influence of the medium on the hyperconjugative and steric effects

The hyperconjugative effect of the methyl group in the para and ortho position of the benzene ring is studied as a function of the medium. The ionization and solution enthalpies of ortho and para toluic acids have been measured in H₂O/DMSO mixtures. A study of the ortho effects by means of the linear combination of the ordinary polar, proximity polar and steric effects has also been performed.The methyl group both in ortho and para position seems to be forced out by the benzene ring at X_dmso= 0.5 mole fraction with a consequent decrease of hyperconjugation effect. A study of enthalpic and entropic contributions to substituent and reaction constants and the proton transfer process from ortho and para derivatives to benzoic acid, compared with the same process in the gaseous phase are also presented.     

Ortho-lithiation reaction of aryl triflones

The ortho-lithiation of substituted arenes is a powerful methodology to synthesize ortho-substituted arenes. While a wide variety of directed metalation groups (DMGs) have been reported, trifluoromethyl sulfone has never been used. We disclose the first example of ortho-lithiation of aryl triflones. We found that the trifluoromethyl sulfonyl group is not only an important structural motif in biologically active molecules and specialty materials, but also an excellent DMG moiety for ortho-metalation reactions. The use of a base that causes steric hindrance, LTMP, is the key for successful transformation to furnish a variety of ortho-substituted aryl triflones in good yields. Further functionalization of resulting ortho-substituted aryl triflones was demonstrated by metal-catalyzed coupling reactions.     

Effect of the Ortho Alkylation of Perylene Bisimides on the Alignment and Self-Assembly Properties

The effect of the ortho alkylation of perylene bisimides on the alignment and self-assembly properties has been studied. It was found that the dichroic properties of perylene bisimides in a liquid crystal host can be reversed with a single synthetic step by ortho alkylation. Furthermore, a solvent-induced growth of ultralong organic n-type semiconducting fibrils from non-ortho-alkylated perylene bisimide was observed. Ortho substitution of the perylene bisimide core alters the mode of fibrillar growth, leading to isotropic crystallization.     

Selective ortho-cleavage of methoxymethyl- and 4-methoxybenzyl ethers

Iodine in methanol has been found to be an effective catalyst system for the cleavage of alkoxymethyl ethers. This catalyst system is particularly useful for the selective removal of ortho-methoxymethyl- and ortho-(4-methoxybenzyl) ethers in the presence of their para-counterparts. Further investigation of various metal salts in methanol for their ability to cleave alkoxymethyl ethers revealed high-valent salts as effective catalysts, presumably through the release of small quantities of HCl.     

Influence of an ortho-sulfinyl group on the configurational stability of α-lithiated aryloxiranes: deuteration of tolylsulfinyl styrene oxides

The influence of the p-tolylsulfinyl group, located at ortho-, meta-, and para-position, on the regio- and stereoselectivity of the deuteration reactions of substituted styrene oxides has been investigated. The sulfinyl group at an ortho-position reduces the configurational stability of α-lithiated styrene oxides, whereas meta- and para-sulfinyl derivatives completely control the regioselectivity only yielding deuterated products at the aromatic ring due to its strong ortho-director effect.     

Efficient microwave-assisted direct C-benzoylation of phenols and naphthols with benzoic acid catalyzed by bismuth triflate under solvent-free or ionic liquid conditions

An efficient and simple route for the synthesis of ortho-hydroxyaryl ketones has been developed. The microwave-assisted direct C-benzoylation of phenols and naphthols in the presence of metal triflates afforded the corresponding ortho-hydroxyaryl ketones in moderate to excellent yields. Bismuth triflate showed the best catalytic performance compared to other metal triflates. The protocol has advantages including short reaction times, high chemoselectivity towards C-acylation, and simple work-up. Additionally, bismuth triflate can be easily recovered and reused several times without significant loss of catalytic performance.     

Synthesis of chiral,non-racemic ferrocene derivatives by ortho-metallation and partial reductive removal of ortho-directing amino groups

Chiral, non-racemic 1,2-disubstituted ferrocenes have been prepared from monosubstituted ferrocene derivatives by amine-mediated ortho-directed reactions and subsequent partial reductive removal of the stereogenic ortho-directing group. It was found that the ortho-directing amino group of 2-substituted derivatives of N,N-dimethylaminoethyl-ferrocene and similar compounds can, after quaternisation with methyl iodide, be reductively removed with sodium borohydride to give 2-substituted methyl- or ethylferrocenes. In most cases the substituents I, Br, COOEt, P(O)Ph₂ and CN tolerate the reaction conditions used. In addition, a few examples are reported that show how the use of LiTMP allows 2-bromo- and especially 2-cyano-substituted derivatives to be further ortho-lithiated and reacted to give 1,2,3-trisubstituted ferrocenes.     

Claisen rearrangements—VII : Novel reactions of the coumarin,tomentin

The structure of tomentin has been confirmed as 5-hydroxy-6,7-dimethoxycoumarin (2), the derived 3,3-dimethylallyl ether giving a para-Claisen rearrangement product. Relief of strain in the corresponding 1,1-dimethylallyl ether has been found to result in a novel regiospecific ortho-Claisen rearrangement occurring on silica at room temperature. The structure 18 of the stable ortho-dienone formed has been confirmed by conversion of the corresponding dehydrodienone (15), obtained from the rearrangement of tomentin 1,1-dimethylpropargyl ether, to alloxanthoxyletin (25).     

Advanced adsorbents for the separation of the ortho- and para-hydrogen spin isomers at cryogenic temperatures

Improved adsorbent types and compositions have been developed for the challenging separation of the ortho- and para-hydrogen spin isomers at 77 K. From a systematic study of commercially available adsorbent types, it has been found that zeolites of type X offer the largest capacity and selectivity towards ortho-hydrogen and that performance is significantly impacted by the cation type and the number of cations present in the zeolite. For the present separation improved performance was obtained with larger Group I cations, especially K and Cs. Another key property of the adsorbents addressed in the present work is the need to control the adsorbent composition to avoid unwanted catalytic conversion of the para- to ortho-hydrogen. A common source of unwanted catalytic activity in many adsorbent compositions was identified as the presence of unwanted transition metal impurities, especially iron associated with the natural clays, commonly employed as binding agents in the commercial agglomerated zeolite products. To avoid this, equivalent adsorbent compositions were agglomerated instead using colloidal silica binding agents which successfully minimize back conversion of the para- to ortho-hydrogen and produced adsorbents with higher capacities and selectivities for the ortho component at the test temperature of 77 K. These advanced adsorbents can be applied in more efficient hydrogen liquefaction processes.     

Metalations utilizing aryllithiums; ortho-functionalization of p-bromoanisole (pBrA)

An ortho-metalation protocol has been developed, which permits the survival of a bromine substituent in p-bromoanisole. Eight derivatives of the generated ortho-lithiated intermediate have been prepared. A neglected metalation concept is being explored here; one which proposes that minimizing the pK_a difference between the aryl substrate and the conjugate acid of the metalating agent will lead to a regiospecific and selective metalation process.     

Regioselective ortho-acetoxylation/methoxylation of N-(2-benzoylphenyl)benzamides via substrate directed C-H activation

A highly regioselective ortho-acetoxylation of N-(2-benzoylphenyl)benzamides has been achieved using a catalytic amount of Pd(OAc)₂ (10 mol %) and a stoichiometric amount of PhI(OAc)₂ in a mixture of acetic anhydride and acetic acid via C-H activation to produce the corresponding 2-acetoxybenzamides in good yields. ortho-Methoxylation has been accomplished using methanol under similar conditions.     

Highly diastereoselective ortho-lithiation of chiral ferrocenecarboxamides

Planar chirality has been introduced into chiral ferrocenecarboxamides via an amide-directed ortho-lithiation with diastereoselectivity of up to 99%. The use of an easily accessible, camphane-based chiral auxiliary as an ortho-directing group led to single diastereoisomers with a variety of electrophiles. The approach allows the preparation of widely applicable ferrocene derivatives.     

Et-duphos-nickel-catalyzed asymmetric arylation of benzaldehyde derivatives bearing an ortho-Me2PhSi group with potassium aryltriolborates

The Ni-catalyzed asymmetric arylation of benzaldehydes bearing an ortho-masked H group with potassium aryltriolborates has been developed. The keys to success were (i) steric tuning of benzaldehyde derivatives with an ortho-Me₂PhSi group, and (ii) the use of potassium aryltriolborates as aryl sources.     

An efficient catalyst for the synthesis of ortho-substituted biaryls by the Suzuki cross-coupling: Triphenylphosphine adduct of cyclopalladated ferrocenylimine

The air and moisture stable triphenylphosphine adduct of cyclopalladated ferrocenylimine 2 has been successfully used in palladium-catalyzed Suzuki cross-coupling for the synthesis of ortho-substituted biaryls in air. In the presence of 0.05 mol% of 2 as catalyst and 3 equivalent of CsF as base in dioxane at 100 °C, ortho-substituted biaryls were synthesized with moderate to high yields in the reactions of 2-methoxy-1-naphthylboronic acid with aryl halides, and 14 new ortho-substituted biaryls were obtained and characterized.     

Rh(I)-catalyzed solvent-free ortho-alkylation of aromatic imines under microwave irradiation

The synthesis of ortho-alkylated ketones through a chelation-assisted Rh (I) catalyzed ortho-alkylation reaction of aromatic imines under microwave activated solvent-free conditions in monomode reactors was performed. These conditions have been also applied to hydroacylation and ortho-alkylation reactions with aldimines.     

Regioselective ortho-nitration of N-phenyl carboxamides and primary anilines using bismuth nitrate/acetic anhydride

An efficient and one-pot synthetic method for the regioselective ortho-nitration of the N-phenyl carboxamides and primary anilines has been developed by using bismuth nitrate and acetic anhydride as the nitrating reagents. Reaction proceeds at room temperature and results in corresponding ortho-nitrated products in moderate to excellent yields. This method provides an operationally simple, regioselective, and efficient access to synthesize o-nitro anilines under the mild conditions.     

Palladium, rhodium and platinum complexes of ortho-xylyl-linked bis-N-heterocyclic carbenes: Synthesis, structure and catalytic activity

New Pd(II), Pt(II) and Rh(I) N-heterocyclic carbene (NHC) complexes containing two NHC units linked by an ortho-xylyl group are described and structurally and spectroscopically characterised. The Pt(II) complexes represent the first examples of Pt-bis(NHC) complexes where the NHC units are linked by an ortho-xylyl group. Functionalisation of the bis(NHC) ligands with heptyl groups has been used as a means of enhancing the solubility of the complexes, in order to facilitate spectroscopic characterisation and catalytic studies. The catalytic activity of the palladium(II) complexes in Heck and Suzuki cross-coupling reactions has been examined to investigate any effects of the diverse structural changes, though these appear to be insignificant.     

2,3-Diarylquinoxaline directed mono ortho-aroylation via cross-dehydrogenative coupling using aromatic aldehydes or alkylbenzenes as aroyl surrogate

2,3-Diarylquinoxaline directed mono ortho-aroylation protocol has been developed using aromatic aldehydes or alkybenzenes as aroyl surrogates. Out of the four available ortho sp² C–H bonds in the two aryl rings of 2,3-diarylquinoxaline one of the C–H bond is selectively ortho-aroylated. The reaction proceeds via the aroyl radical path in the case of aromatic aldehydes while the alkylbenzenes follow either an aroyl radical or a benzyl radical path. Varieties of functional groups present as substituents in 2,3-diarylquinoxalines, aromatic aldehydes and alkylbenzenes are tolerated under the present reaction conditions.     

Heats of atomization and resonance energy of some ortho-substituted benzoic acids

An experimental determination of heats of atomization of some ortho-substituted benzoic acids has been performed by combustion and differential scanning calorimetry. Resonance energy was calculated by the difference between the heat of atomization in the gas phase and the sum of the bond energies of a fixed bond structure for a resonating molecule. As the van der Waals radii of the ortho-substituent increased a decrease in resonance energy was observed.