Functionalization of Hexa‐peri‐hexabenzocoronenes: Investigation of the Substituent Effects on a Superbenzene

We have demonstrated that the iridium‐catalyzed direct borylation of hexa‐peri‐hexabenzocoronene (HBC) enables regioselective introduction of boryl groups to the para‐, ortho‐, and meta‐substituted HBCs in high yields. The boryl groups have been transformed into various functionalities such as hydroxy, cyano, ethynyl, and amino groups. We have elucidated that the substituents significantly influence the photophysical properties of HBCs to enhance fluorescence quantum yields. DFT calculations revealed that the origin of the substituent effect is the lift in degeneracy in the frontier orbitals by an interaction with electron‐donating and electron‐withdrawing substituents at the para‐ and ortho‐positions. The change in molecular orbitals results in an increase of the transition probability from the S₀→S₁ states. In addition, the two‐photon absorption cross‐section values of para‐substituted HBCs are significantly larger than those of ortho‐ and meta‐substituted HBCs.     

Ethyl 2‐form­amido‐2‐(4‐iodo­benzyl)‐3‐(4‐iodo­phenyl)­propionate and ethyl 2‐(3‐bromo­benzyl)‐3‐(3‐bromo­phenyl)‐2‐form­amidopropionate

The title compounds, C₁₉H₁₉I₂NO₃ and C₁₉H₁₉Br₂NO₃, are derivatives of α‐amino­isobutyric acid with halogen substituents at the para and meta positions, respectively. The ethoxycarbonyl and formamide side chains attached to the C_α atom of the mol­ecule adopt extended and folded conformations, respectively. The crystal structures are stabilized by N—H⃛O, C—H⃛O, C—Br⃛O and C—I⃛O interactions.     

11‐Vertex arachno‐Clusters with an NB10, SNB9, and SeNB9 Skeleton

One of the two bridging protons of the aza‐nido‐decaboranes RNB₉H₁₀X can be removed by certain bases to give nido‐anions [RNB₉H₉X]^– [R/X = H/H ( 1 a ), Ph/H ( 1 b ), p‐MeC₆H₄/H ( 1 c ), Bzl/H ( 1 d ), H/N₃ ( 1 ′ a )]; the stericly demanding base 1,8‐bis(dimethylamino)naphthalene (“proton sponge”, ps) is ideal. In the case of tBu anion, the deprotonation (→ C₄H₁₀) may be accompanied by a hydridation (→ C₄H₈), yielding the arachno‐anions [RNB₉H₁₁X]^– ( 2 a , b , d , 2 ′ a ); these are the main products, when stericly non‐demanding bases like H^– are applied. The Lewis acid BH₃ is added to 1 a and 1 ′ a to give the aza‐arachno‐undecaborates HNB₁₀H₁₂X [X = H ( 3 a ), N₃ (in position 2) ( 3 ′ a )]. Thia‐ and selenaaza‐arachno‐undecaborates, [S(RN)B₉H₁₀]^– ( 4 b , c ) and [Se(RN)B₉H₁₀]^– ( 4 ′ b , c ), are obtained from 1 b , c by the addition of sulfur or selenium, respectively. The methylation of the anions 4 c and 4 ′ c gives the thia‐ and selenaazaarachno‐undecaboranes (MeS)(RN)B₉H₁₀ ( 5 c ) and (MeSe)(RN)B₉H₁₀ ( 5 ′ c ), respectively. The action of HBF₄ on the arachno‐borates [HNB₁₀H₁₂X]^– ( 3 a , 3 ′ a ) leads to a mixture of nido‐HNB₉H₁₀X and nido‐HNB₁₀H₁₁X by the elimination of BH₃ or H₂, respectively; the aza‐nido‐decaborane predominates in the case of 3 ′ a and the aza‐nido‐undecaborane in the case of 3 a . The action of HBF₄ on the anion 4 c yields the hypho‐undecaborate [S(RN)B₉H₁₀F₂]^– ( 6 c ). The structures of the products are elucidated on the basis of ¹H and ¹¹B NMR spectra, supported by 2D COSY and HMQC techniques. Two types of 11‐vertex‐arachno structures and an 11‐vertex‐hypho structure are found for the products. The crystal structures of 5 c and [Hps] 6 c · CH₂Cl₂ are reported.     

Computational study on the comparative synthesis of energetic FOX‐7 derivatives

Ethene and two kinds of nitrating reagents (HNO₃ and N₂O₅) were included in respective molecular systems, which progressed through a two‐stage electrophilic and free radical nitrosubstitution, resulting in the corresponding nitroethene compounds. Subsequent halogenation (using Cl₂ and Br₂) and amination (using ammonia) were then performed, also by electrophilic and radical substitution, to produce the target 1,1‐diamino‐2,2‐dinitroethene (FOX‐7) derivatives. All transition state species were identified using a two‐ or three‐structure Synchronous Transit‐Guided Quasi‐Newton between the Cartesian coordinates of the related molecular systems at specific reaction stages. The modeling results suggest that N₂O₅ is the better agent for nitration and bromine is suitable for use in halogenation. The comparable activation energies throughout the reaction stages were considered to imply the most feasible pathways of FOX‐7 synthesis. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Five (1H‐pyrrol‐2‐yl)­pyridines

The title (1H‐pyrrol‐2‐yl)­pyridines, C₉H₈N₂, substituted at the ortho, meta, and para positions of the pyridine ring all have hydrogen‐bonded arrangements with geometrically similar, nearly linear, N(pyrrole)—H⋯N(pyridine) hydrogen bonds of average length. The graph sets for the ortho, meta, and three para polymorphs are R(10), C(6), C(7), C(7), and R(28), respectively.     

Aza‐nido‐dodecaboranes and ‐borates from Aza‐closo‐dodecaboranes by the Addition of Neutral or Anionic Bases: Mechanism

The addition of neutral (L = py, NEt₃, NHEt₂, NH₂tBu) and anionic Lewis bases (X^‐ = OH^‐, Br^‐, N₃^‐, Me^‐, NHBu ^‐, NHtBu^‐, [FeCp(CO)₂]^‐) to aza‐closo‐dodecaboranes RNB₁₁H₁₁ ( 1 ) or to derivatives thereof with boron bound non‐hydrogen ligands yields nido‐clusters RNB₁₁H₁₁L or [RNB₁₁H₁₁X]^‐ or derivatives thereof, respectively, the non‐planar pentagonal aperture N—B4—B9—B8—B5 of which hosts a B8—B9 hydrogen bridge. The base is either bound to B8 ( 3 )or B4 ( 5 )or B2( 7 ). The structures of these adducts are concluded from ¹H and ¹¹B NMR including 2D‐NMR spectra, and in the case of MeNB₁₁H₁₁(NHEt₂) (type 3 ) also by a crystal structure analysis. With two of the adducts MeNB₁₁H₁₁L (L = py, NHEt₂), isomers of the type 3 , 5 , and 7 , and with two of the adducts, MeNB₁₁H₁₁(NH₂tBu) and {MeNB₁₁H₁₁[FeCp(CO)₂]}^‐, isomers of the type 3 and 7 could be identified. The position of boron‐bound ligands during the addition of bases to 1 shows, that only vertices of the ortho‐belt of 1 are involved in the opening process. A mechanism is made plausible that starts by the attack of the base at B2 of 1 and opening of the N‐B2 bond, denoted as a [3c, 1c]‐collocation, to give 2 with an endo‐H atom, whose migration into an adjacent bridge position and opening of a second B—N bond, denoted as a [3c, 2c]‐translocation, gives 3 ; this isomer can be transformed into 7 by a sequence of [3c, 2c]‐translocations via the isomers 4 , 5 , and 6 . The chiral type 3 species MeNB₁₁H₁₁L with L = NHEt₂, NH₂tBu undergo a rapid enantiomerization, for whose mechanism the exchange of the bridging and the amine‐H atom has been made plausible.     

Hydrogen bonding in 4‐nitrobenzene‐1,2‐diamine and two hydrohalide salts

The structures of 4‐nitrobenzene‐1,2‐diamine [C₆H₇N₃O₂, (I)], 2‐amino‐5‐nitroanilinium chloride [C₆H₈N₃O₂⁺·Cl⁻, (II)] and 2‐amino‐5‐nitroanilinium bromide monohydrate [C₆H₈N₃O₂⁺·Br⁻·H₂O, (III)] are reported and their hydrogen‐bonded structures described. The amine group para to the nitro group in (I) adopts an approximately planar geometry, whereas the meta amine group is decidedly pyramidal. In the hydrogen halide salts (II) and (III), the amine group meta to the nitro group is protonated. Compound (I) displays a pleated‐sheet hydrogen‐bonded two‐dimensional structure with R₂²(14) and R₄⁴(20) rings. The sheets are joined by additional hydrogen bonds, resulting in a three‐dimensional extended structure. Hydrohalide salt (II) has two formula units in the asymmetric unit that are related by a pseudo‐inversion center. The dominant hydrogen‐bonding interactions involve the chloride ion and result in R₄²(8) rings linked to form a ladder‐chain structure. The chains are joined by N—H...Cl and N—H...O hydrogen bonds to form sheets parallel to (010). In hydrated hydrohalide salt (III), bromide ions are hydrogen bonded to amine and ammonium groups to form R₄²(8) rings. The water behaves as a double donor/single acceptor and, along with the bromide anions, forms hydrogen bonds involving the nitro, amine, and ammonium groups. The result is sheets parallel to (001) composed of alternating R₅⁵(15) and R₆⁴(24) rings. Ammonium N—H...Br interactions join the sheets to form a three‐dimensional extended structure. Energy‐minimized structures obtained using DFT and MP2 calculations are consistent with the solid‐state structures. Consistent with (II) and (III), calculations show that protonation of the amine group meta to the nitro group results in a structure that is about 1.5 kJ mol⁻¹ more stable than that obtained by protonation of the para‐amine group. DFT calculations on single molecules and hydrogen‐bonded pairs of molecules based on structural results obtained for (I) and for 3‐nitrobenzene‐1,2‐diamine, (IV) [Betz & Gerber (2011). Acta Cryst. E 67 , o1359] were used to estimate the strength of the N—H...O(nitro) interactions for three observed motifs. The hydrogen‐bonding interaction between the pairs of molecules examined was found to correspond to 20–30 kJ mol⁻¹.     

N‐(4‐Biphenylmethyl)imidazoles as Potential Therapeutics for the Treatment of Prostate Cancer: Metabolic Robustness Due to Fluorine Substitution?

3,3′,5,5′‐ And 2,2′,6,6′‐tetrafluoro‐substituted 1‐[(1,1′‐biphenyl]‐4‐yl)methyl]‐1H‐imidazoles were synthesized as inhibitors of 17α‐hydroxylase‐C17,20‐lyase (P450 17, CYP 17). P450 17 is the key enzyme of androgen biosynthesis. Its inhibition is a novel therapeutic approach for treatment of prostate cancer. To increase the so‐far insufficient in vivo lifetime of such compounds, the metabolically sensitive positions were blocked by F‐substitution. The meta‐ and ortho‐F‐substituted compounds were prepared by selective metallation or halogen/metal permutation reactions performed on symmetrically substituted 1,1′‐biphenyls. Compared with the halogen‐free compounds, the ortho‐F‐substituted derivatives did not match the activity, whereas the meta‐F‐substituted isomers equaled or surpassed the latter.     

Synthesis of Densely Functionalised 5‐Halogen‐1,3‐oxazin‐2‐ones by Halogen‐Mediated Regioselective Cyclisation of N‐Cbz‐Protected Propargylic Amines: A Combined Experimental and Theoretical Study

A very efficient synthesis of 5‐halogen‐1,3‐oxazin‐2‐ones has been accomplished by the halocyclisation reaction of chiral nonracemic N‐carbobenzyloxy (N‐Cbz)‐protected propargylic amines by using I₂, Br₂ and Cl₂ as electrophile sources. The nature of the halogen influences the reaction time and yield. However, in all cases the reaction is totally regioselective taking place through a 6‐endo‐dig process regardless of the nature of the halogen and of the substituents in the starting material. To rationalise the experimental results, theoretical studies at the B3LYP/6‐311G* level have been performed.     

meta‐ and para‐Phenylenediamine‐Fused Porphyrin Dimers: Synthesis and Magnetic Interactions of Their Dication Diradicals

meta‐ and para‐Phenylenediamine‐fused nickel(II) porphyrin dimers were synthesized by S_NAr reaction of meso,β,β‐trichloro nickel(II) porphyrin with meta‐ and para‐phenylenediamines and subsequent Pd‐catalyzed intramolecular C?H arylation. Their tetrachlorinated dication diradicals are very stable, allowing SQUID magnetometry and revealing clear open‐shell characters for both meta and para isomers with ferro‐ and anti‐ferromagnetic interactions, respectively. The nitrogen analogue of Thiele's hydrocarbon usually displays predominant closed‐shell nature but its hidden diradical characters increase either in a twisted conformation or upon insertion of an additional phenylene spacer. The observed distinct diradical nature of the para‐congener indicates that diradical properties can be enhanced also by efficient spin delocalization.     

Computational study of FOX‐7 synthesis in a solvated reaction system

Ethene and two kinds of nitrating reagents (HNO₃ and N₂O₅) in a variety of solvents were included in respective molecular systems, and each underwent a two‐stage electrophilic and free radical nitro‐substitution reaction to obtain the corresponding nitroethene compounds. Subsequent halogenation (using Cl₂ and Br₂) and amination (using NH₃) were then performed in solvents, also by electrophilic and radical substitution, to produce the desired 1,1‐diamino‐2,2‐dinitroethene (FOX‐7) derivatives. The reaction energy barrier in the nitration stage for obtaining each kind of mononitro ethene exhibited a stepwise decreasing trend when the reaction was carried out in H₂O‐solvated and CH₃OH‐solvated systems, no matter what nitrating agent was used. Related energy barrier data showed that the nitration reaction is more feasible in an H₂O‐solvated than a CH₃OH‐solvated system. The modeling results suggested that N₂O₅ is the better agent for nitration to proceed in water, bromine is suitable for halogenation, and the bromine derivatives are convenient for further amination in an H₂O‐solvated system. © 2010 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Facile synthesis,characterisation and anti‐inflammatory activities of ferrocenyl ester derivatives of 4‐arylidene‐5‐imidazolinones

This article describes the synthesis, optoelectronic properties and anti‐inflammatory activities of a series of seven ferrocenyl ester‐linked 4‐arylidene‐5‐imidazolinone conjugates. Three different types of ortho‐, meta‐ and para‐substituted ferrocenyl esters have been prepared. Their UV–Vis spectra and electrochemical studies are described. The structure of one of the conjugates was confirmed by single‐crystal X‐ray diffraction study. These conjugates exhibited moderate anti‐inflammatory activities.     

Reactions of Di(tert‐butyl)diazomethane with Acceptor‐Substituted Ethylenes

Di(tert‐butyl)diazomethane ( 4 ) is a nucleophilic 1,3‐dipole with strong steric hindrance at one terminus. In its reaction with 2,3‐bis(trifluoromethyl)fumaronitrile ((E)‐ BTE ), a highly electrophilic tetra‐acceptor‐substituted ethene, an imino‐substituted cyclopentene 9 is formed as a 1 : 2 product. The open‐chain zwitterion 10 , assumed as intermediate, adds the second molecule of (E)‐ BTE . The ¹⁹F‐ and ¹³C‐NMR spectra allow the structural assignment of two diastereoisomers, 9A and 9B . The zwitterion 10 can also be intercepted by dimethyl 2,3‐dicyanofumarate ( 11 ) and furnishes diastereoisomeric cyclopentenes 12A and 12B ; an X‐ray‐analysis of 12B confirms the ‘mixed’ 1 : 1 : 1 product. Competing is an (E)‐ BTE ‐catalyzed decomposition of 4 to give 2,3,4,4‐tetramethylpent‐1‐ene ( 7 )+N₂; the reaction of (E)‐ BTE with a trace of water appears to be responsible for the chain initiation. The H₂SO₄‐catalyzed decomposition of diazoalkane 4 , indeed, produced the alkene 7 in high yield. The attack on the hindered diazoalkane 4 by 11 is slower than that by (E)‐ BTE ; the zwitterionic intermediate 21 undergoes cyclization and furnishes the tetrasubstituted furan 22 . In fumaronitrile, electrophilicity and steric demand are diminished, and a 1,3‐cycloaddition produces the 4,5‐dihydro‐1H‐pyrazole derivative 25 . The reaction of 4 with dimethyl acetylenedicarboxylate leads to pyrazole 29 +isobutene.     

A ‘meta effect’ in the fragmentation reactions of ionised alkyl phenols and alkyl anisoles

The competition between benzylic cleavage (simple bond fission [SBF]) and retro‐ene rearrangement (RER) from ionised ortho, meta and para RC₆H₄OH and RC₆H₄OCH₃ (R = n‐C₃H₇, n‐C₄H₉, n‐C₅H₁₁, n‐C₇H₁₅, n‐C₉H₁₉, n‐C₁₅H₃₁) is examined. It is observed that the SBF/RER ratio is significantly influenced by the position of the substituent on the aromatic ring. As a rule, phenols and anisoles substituted by an alkyl group in meta position lead to more abundant methylene‐2,4‐cyclohexadiene cations (RER fragmentation) than their ortho and para homologues. This ‘meta effect’ is explained on the basis of energetic and kinetic of the two reaction channels. Quantum chemistry computations have been used to provide estimate of the thermochemistry associated with these two fragmentation routes. G3B3 calculation shows that a hydroxy or a methoxy group in the meta position destabilises the SBF and stabilises the RER product ions. Modelling of the SBF/RER intensities ratio has been performed assuming two single reaction rates for both fragmentation processes and computing them within the statistical RRKM formalism in the case of ortho, meta and para butyl phenols. It is clearly demonstrated that, combining thermochemistry and kinetics, the inequality (SBF/RER)_meta < (SBF/RER)_ortho < (SBF/RER)_para holds for the butyl phenols series. It is expected that the ‘meta effect’ described in this study enables unequivocal identification of meta isomers from ortho and para isomers not only of alkyl phenols and alkyl anisoles but also in other alkyl benzene series. Copyright © 2012 John Wiley & Sons, Ltd.     

Undecahalo‐closo‐undecaborates [B11Hal11]2–

The closo‐undecaborate A₂[B₁₁H₁₁] (A = NBzlEt₃) can be halogenated with excess N‐chlorosuccine imide, bromine or iodine, respectively, to give the perhalo‐closo‐undecaborates A₂[B₁₁Hal₁₁] (Hal = Cl, Br, I). The chlorination in the 11 : 1 ratio of the reagents yields A₂[B₁₁HCl₁₀], whose subsequent iodination makes A₂[B₁₁Cl₁₀I] available. The three type [B₁₁Hal₁₁]^2– anions show only one and the two type [B₁₁Cl₁₀X]^2– anions (X = H, I) only two ¹¹B NMR peaks in the ratio 10 : 1, thus exhibiting the same degenerate rearrangement of the octadecahedral B₁₁ skeleton as is well‐known for [B₁₁H₁₁]^2–. The crystal structure analysis of A₂[B₁₁Br₁₁] and A₂[B₁₁I₁₁] reveals a rigid octadecahedral skeleton in the solid state, up to 330 K, whose B–B bond lengths deviate more or less from the idealized C_2v gas phase structure, but are in good accordance with the distances of A₂[B₁₁H₁₁]. Electrochemical experiments elucidate the mechanism of the known oxidation of [B₁₁H₁₁]^2– to give [B₂₂H₂₂]^2–: A first one‐electron transfer is followed by the dimerization of the [B₁₁H₁₁]^– monoanion, whereas neutral B₁₁H₁₁, a presumably most reactive species, does not play a role as an intermediate. The electrochemical oxidation of [B₁₁Hal₁₁]^2– anions also starts with a one‐electron transfer, which is perfectly reversible only in the case of Hal = Br. There is no electrochemical indication for the formation of [B₂₂Hal₂₂]^2–. The neutral species B₁₁Hal₁₁ should be a short‐lived, very reactive species.     

Dimerization of a mixed‐carbene PdII dibromide complex by elemental iodine

A monomeric Pd^II complex bearing a mixed carbocyclic/N‐heterocyclic carbene ligand and two bromides was reacted with an excess of elemental iodine, which resulted in the surprising removal of one bromide ligand and dimerization of the mixed‐carbene complex to form di‐μ‐bromido‐bis{[1‐(cyclohepta‐2,4,6‐trien‐2‐yl‐1‐ylidene‐κC ¹)‐3‐(2,6‐diisopropylphenyl)imidazol‐2‐ylidene]palladium(II)} bis(pentaiodide) dichloromethane monosolvate, [Pd₂Br₂(C₂₂H₂₄N₂)₂](I₅)₂·CH₂Cl₂. The dimeric complex features a slightly distorted square‐planar core of two Pd^II centres bridged by two bromide ligands, which lie in the same plane as the seven‐ and five‐membered rings of the bidentate carbene ligand. The counter‐ions in the single crystal were found to be pentaiodide monoanions featuring their typical V‐shape, whereas for the bulk material, a mixture of Br/I interhalides is proposed.     

Crystal structure and photoreactivity of a halogen‐bonded cocrystal based upon 1,2‐diiodoperchlorobenzene and 1,2‐bis(pyridin‐4‐yl)ethylene

The formation of a photoreactive cocrystal based upon 1,2‐diiodoperchlorobenzene ( 1,2‐C₆I₂Cl₄ ) and trans‐1,2‐bis(pyridin‐4‐yl)ethylene ( BPE ) has been achieved. The resulting cocrystal, 2( 1,2‐C₆I₂Cl₄ )·( BPE ) or C₆Cl₄I₂·0.5C₁₂H₁₀N₂, comprises planar sheets of the components held together by the combination of I…N halogen bonds and halogen–halogen contacts. Notably, the 1,2‐C₆I₂Cl₄ molecules π‐stack in a homogeneous and face‐to‐face orientation that results in an infinite column of the halogen‐bond donor. As a consequence of this stacking arrangement and I…N halogen bonds, molecules of BPE also stack in this type of pattern. In particular, neighbouring ethylene groups in BPE are found to be parallel and within the accepted distance for a photoreaction. Upon exposure to ultraviolet light, the cocrystal undergoes a solid‐state [2 + 2] cycloaddition reaction that produces rctt‐tetrakis(pyridin‐4‐yl)cyclobutane ( TPCB ) with an overall yield of 89%. A solvent‐free approach utilizing dry vortex grinding of the components also resulted in a photoreactive material with a similar yield.     

Non‐Isomorphic Chlorine—Bromine Substitution in the Copper(I) Halide π‐Complexes with 1‐Allyl‐4‐aminopyridinium

By alternating‐current electrochemical synthesis crystals of {Cu[H₂NC₅H₄N(C₃H₅)]Br₂} ˙ H₂O ( I ), {Cu[H₂NC₅H₄N(C₃H₅)]Br_0.65Cl_1.35} ˙ H₂O ( II ) and {Cu[H₂NC₅H₄N(C₃H₅)]Cl₂} ( III ) π‐complexes have been obtained and structurally investigated. The I and II compounds are isostructural and crystallize in a monoclinic sp. gr. P2₁/c, I : a = 7.359(2)Å, b = 12.3880(6)Å, c = 13.637(3)Å, β = 107.03(1)°, V = 1188.7(4)ų, Z = 4 for C₈H₁₃N₂OBr₂Cu composition, R = 0.0293 for 2140 reflections. II : a = 7.2771(6)Å, b = 12.3338(3)Å, c = 13.4366(7)Å, β = 107.632(2)°, V = 1149.3(1)ų, Z = 4 for C₈H₁₃N₂Br_0.65Cl_1.35Cu composition, R = 0.0463 for 2185 reflections. Metal and halogen atoms form centrosymmetric Cu₂X₄ dimers. Each copper atom is surrounded by three halogen atoms and by a weakly bonded C=C‐group of the onium moiety. Isolated {Cu[H₂NC₅H₄N(C₃H₅)]}₂X₄ dimers are combined into a three‐dimensional network due to a bridging function of water molecules via a system of rather strong hydrogen bonds. Chlorine derivative III crystallizes in another structure type: sp. gr. C2/c, a = 21.568(7)Å, b = 7.260(2)Å, c = 13.331(3)Å, β = 95.65(2)°, V = 2077(2)ų, Z = 8 for C₈H₁₁N₂Cl₂Cu composition. Copper atom, included in CuCl₂^— isolated fragment, is coordinated to a C=C‐bond of ligand moiety. N‐H…Cl hydrogen bonds unite Cu[H₂NC₅H₄N(C₃H₅)]Cl₂ subunits into infinite ribbons. π‐Interaction in III appears to be more effective than in I and II .     

A Convenient Synthesis of N‐Aryl Benzamides by Rhodium‐Catalyzed ortho‐Amidation and Decarboxylation of Benzoic Acids

The rhodium‐catalyzed amidation of substituted benzoic acids with isocyanates by directed C?H functionalization followed by decarboxylation to afford the corresponding N‐aryl benzamides is demonstrated, in which the carboxylate serves as a unique, removable directing group. Notably, less common meta‐substituted N‐aryl benzamides are generated readily from more accessible para‐ or ortho‐substituted groups by employing this strategy.     

Photoisomerization of Trans Ortho‐, Meta‐, Para‐Nitro Diarylbutadienes: A Case of Regioselectivity

A series of ortho‐, meta‐ and para‐substituted trans‐nitro aryl (phenyl and pyridyl) butadienes have been synthesized and characterized. The effect of substitution and positional selectivity on their fluorescence and photoisomerization were systematically investigated. Among all dienes, meta‐ and para‐nitro phenyl‐substituted derivatives exhibit remarkable solvatochromic emission shifts due to intramolecular charge transfer. On the other hand, ortho derivatives undergo regioselective isomerization upon photoexcitation in contrast to inefficient isomerization of para and meta nitro‐substituted dienes. Single crystal X‐ray analysis revealed existence of intramolecular hydrogen bonding between the nitro group and the hydrogen of the proximal double bond. This restricts the rotation of the proximal double bond thereby allowing regioselective isomerization. The observations were also supported by NMR spectroscopic studies.