2‐Ethyl‐6‐methylpyridin‐3‐ol and its salt bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate

The title compounds, C₈H₁₁NO, (I), and 2C₈H₁₂NO⁺·C₄H₄O₄²⁻, (II), both crystallize in the monoclinic space group P2₁/c. In the crystal structure of (I), intermolecular O—H...N hydrogen bonds combine the molecules into polymeric chains extending along the c axis. The chains are linked by C—H...π interactions between the methylene H atoms and the pyridine rings into polymeric layers parallel to the ac plane. In the crystal structure of (II), the succinate anion lies on an inversion centre. Its carboxylate groups interact with the 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium cations via intermolecular N—H...O hydrogen bonds with the pyridine ring H atoms and O—H...O hydrogen bonds with the hydroxy H atoms to form polymeric chains, which extend along the [01] direction and comprise R₄⁴(18) hydrogen‐bonded ring motifs. These chains are linked to form a three‐dimensional network through nonclassical C—H...O hydrogen bonds between the pyridine ring H atoms and the hydroxy‐group O atoms of neighbouring cations. π–π interactions between the pyridine rings and C—H...π interactions between the methylene H atoms of the succinate anion and the pyridine rings are also present in this network.     

Recent Advances in Radical‐Mediated C—C Bond Fragmentation of Non‐Strained Molecules

The carbon‐carbon (C—C) σ‐bonds construct the fundamental frameworks of organic molecules. The direct functionalization of C—C bonds represents one of the most efficient and step‐economical transformations in synthetic chemistry. The past few decades have witnessed the fast development of transition‐metal mediated C—C bond activation. In contrast, the radical‐promoted C—C bond cleavage has received relatively less attention. As the occurrence of ring strain significantly facilitates the fission of cyclic C—C bonds via radical approaches, the strain relief‐driven C—C bond activation mostly relies on the three‐ and four‐membered rings. The C—C activation of non‐strained molecules such as medium‐ or large‐sized rings and linear alkanes remains challenging. In this review, we will focus on the recent advances in radical‐mediated C—C bond activation of non‐strained molecules. Herein, the alkoxy‐ and iminyl‐radical triggered scission of non‐strained C—C bonds and C—C cleavage via the strategy of remote functional group migration is summarized.     

Supramolecular structures of three isomeric 4‐(methyl­phenylamino)­pyridine‐3‐sulfonamides

The structures of the three title isomers, namely 4‐(2‐methyl­anilino)pyridine‐3‐sulfonamide, (I), 4‐(3‐methyl­anilino)pyridine‐3‐sulfonamide, (II), and 4‐(4‐methyl­anilino)pyridine‐3‐sulfonamide, (III), all C₁₂H₁₃N₃O₂S, differ in their hydrogen‐bonding arrangements. In all three mol­ecules, the conformation of the 4‐amino­pyridine‐3‐sulfon­amide moiety is conserved by an intra­molecular N—H⋯O hydrogen bond and a C—H⋯O inter­action. In the supra­mol­ecular structures of all three isomers, similar C(6) chains are formed via inter­molecular N—H⋯N hydrogen bonds. N—H⋯O hydrogen bonds lead to C(4) chains in (I), and to R₂²(8) centrosymmetric dimers in (II) and (III). In each isomer, the overall effect of all hydrogen bonds is to form layer structures.     

N,N′‐Bis(2‐pyridyl)benzene‐1,2‐diamine

Hindered rotation about the partial double C—N bonds between the amine and pyridine moieties in the title mol­ecule, C₁₆H₁₄N₄, results in two different conformations of the N‐aryl‐2‐amino­pyridine units. One, assuming an E conformation, is involved in a pair of N—H⋯N hydrogen bonds that generate a centrosymmetric (8) motif. The second, adopting a Z conformation, is not engaged in any hydrogen bonding and is flattened, the dihedral angle between the benzene and pyridine rings being 12.07 (7)°. This conformation is stabilized by an intramolecular C—H⋯N interaction [C⋯N = 2.9126 (19) Å, H⋯N = 2.31 Å and C—H⋯N = 120°].     

Hydrogen‐bonded assembly in six closely related pyrazolo[3,4‐b]pyridine derivatives; a simple chain,three types of chains of rings and a complex sheet structure

Six closely related pyrazolo[3,4‐b]pyridine derivatives, namely 6‐chloro‐3‐methyl‐1,4‐diphenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₄ClN₃O, (I), 6‐chloro‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O, (II), 6‐chloro‐4‐(4‐chlorophenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃Cl₂N₃O, (III), 4‐(4‐bromophenyl)‐6‐chloro‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃BrClN₃O, (IV), 6‐chloro‐4‐(4‐methoxyphenyl)‐3‐methyl‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₁H₁₆ClN₃O₂, (V), and 6‐chloro‐3‐methyl‐4‐(4‐nitrophenyl)‐1‐phenylpyrazolo[3,4‐b]pyridine‐5‐carbaldehyde, C₂₀H₁₃ClN₄O₃, (VI), which differ only in the identity of a single small substituent on one of the aryl rings, crystallize in four different space groups spanning three crystal systems. The molecules of (I) are linked into a chain of rings by a combination of C—H...N and C—H...π(arene) hydrogen bonds; those of (II), (IV) and (V), which all crystallize in the space group P, are each linked by two independent C—H...O hydrogen bonds to form chains of edge‐fused rings running in different directions through the three unit cells; the molecules of (III) are linked into complex sheets by a combination of two C—H...O hydrogen bonds and one C—H...π(arene) hydrogen bond; finally, the molecules of (VI) are linked by a single C—H...O hydrogen bond to form a simple chain.     

Hydro­gen‐bonded supramolecular motifs in 4,4′‐bipyridinium 8‐hydroxy‐7‐iodo­quinoline‐5‐sulfonate dihydrate

In the title compound, C₁₀H₉N₂⁺·C₉H₅INO₄S⁻·2H₂O, the 4,4′‐bi­pyridine mol­ecule is protonated at one of the pyridine N atoms. These moieties self‐assemble into a supramolecular chain along the a axis through N—H⋯N hydrogen bonds. The quinolinol OH group acts as a donor with respect to a sulfonate O atom [O—H⋯O(sulfonate)] and acts as an acceptor with respect to a C—H group of ferron [C—H⋯O(hydroxy)], forming a supramolecular chain along the b axis. These two types of supramolecular chains (one type made up of bi­pyridine motifs and the other made up of sulfoxine motifs) interact viaπ–π stacking, generating a three‐dimensional framework. These chains are further crosslinked by C—­H⋯O hydrogen bonds and O—H⋯O hydrogen bonds involving water mol­ecules.     

4′‐Iodo‐2,2′:6′,2′′‐terpyridine

In the nearly planar title compound, C₁₅H₁₀IN₃, the three pyridine rings exhibit transoid conformations about the interannular C—C bonds. Very weak C—H...N and C—H...I interactions link the molecules into ribbons. Significant π–π stacking between molecules from different ribbons completes a three‐dimensional framework of intermolecular interactions. Four different packing motifs are observed among the known structures of simple 4′‐substituted terpyridines.     

Supramolecular aggregation in three 4‐aryl‐6‐(1H‐indol‐3‐yl)‐3‐methyl‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitriles

Both 6‐(1H‐indol‐3‐yl)‐3‐methyl‐4‐(4‐methylphenyl)‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile and 6‐(1H‐indol‐3‐yl)‐3‐methyl‐4‐(4‐methoxyphenyl)‐1‐phenyl‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile crystallize from dimethylformamide solutions as stoichiometric 1:1 solvates, viz. C₂₉H₂₁N₅·C₃H₇NO, (I), and C₂₉H₂₁N₅O·C₃H₇NO, (II), respectively; however, 6‐(1H‐indol‐3‐yl)‐3‐methyl‐1‐phenyl‐4‐(3,4,5‐trimethoxyphenyl)‐1H‐pyrazolo[3,4‐b]pyridine‐5‐carbonitrile, C₃₁H₂₅N₅O₃, (III), crystallizes in the unsolvated form. The heterocyclic components of (I) are linked by C—H...π(arene) hydrogen bonds to form cyclic centrosymmetric dimers, from which the solvent molecules are pendent, linked by N—H...O hydrogen bonds. In (II), the heterocyclic components are linked by a combination of C—H...N and C—H...π(arene) hydrogen bonds into chains containing two types of centrosymmetric ring, and the pendent solvent molecules are linked to these chains by N—H...O hydrogen bonds. Molecules of (III) are linked into simple C(12) chains by an N—H...O hydrogen bond, and these chains are weakly linked into pairs by an aromatic π–π stacking interaction.     

Dichloro­[(1E,1′E)‐1,1′‐(pyridine‐2,6‐diyl)diethanone bis­(O‐methyl­oxime)‐κ3N1,N2,N6]copper(II)

In the title compound, [CuCl₂(C₁₁H₁₅N₃O₂)], the Cu^II ion is five‐coordinated in a strongly distorted trigonal–bipyramidal arrangement, with the two methyl­oxime N atoms located in the apical positions, and the pyridine N and the Cl atoms located in the basal plane. The two axial Cu—N distances are almost equal (mean 2.098 Å) and are substantially longer than the equatorial Cu—N bond [1.9757 (15) Å]. It is observed that the N(oxime)—M—N(pyridine) bond angle for five‐membered chelate rings of 2,6‐diacetyl­pyridine dioxime complexes is inversely related to the magnitude of the M—N(pyridine) bond. The structure is stabilized by intra‐ and inter­molecular C—H⋯Cl hydrogen bonds which involve the methyl H atoms, except for one of the two acetyl­methyl groups.     

Pentacarbonyl(4‐phenylpyridine)­tungsten(0) and pentacarbonyl(2‐phenylpyridine)chromium(0)

In penta­carbonyl(4‐phenyl­pyridine)­tungsten(0), [W­(C₁₁H₉N)(CO)₅], the mol­ecules have mm site symmetry and the pyridine ligand, with m symmetry, is completely planar. In penta­carbonyl(2‐phenyl­pyridine)­chromium(0), [Cr(C₁₁­H₉N)(CO)₅], the mol­ecules are in general positions and the phenyl and pyridine rings of the ligand are twisted by 67.7 (3)° with respect to one another by rotation about the C—C bond joining them. In both compounds, the axial M—C_carbonyl bond trans to the M—N_ligand bond is significantly shorter than the equatorial M—C_carbonyl bonds.     

Di‐μ‐chlorido‐bis[chlorido(4′‐p‐tolyl‐2,2′:6′,2′′‐terpyridine‐κ3N,N′,N′′)nickel(II)]: a supramolecular system constructed by C—H...Cl interactions

The title complex, [Ni₂Cl₄(C₂₂H₁₇N₃)₂], was synthesized solvothermally. The molecule is a centrosymmetric dimer with the unique Ni^II centre in a distorted octahedral N₃Cl₃ coordination environment. The chloride bridges are highly asymmetric. In the 4′‐p‐tolyl‐2,2′:6′,2′′‐terpyridine ligand, the p‐tolyl group is perfectly coplanar with the attached pyridine ring, and this differs from the situation found in previously reported compounds; however, there are no π–π interactions between the ligands. The terminal Cl atom forms four intermolecular C—H...Cl hydrogen bonds with one methyl and three methine groups. The methyl group also forms intermolecular C—H...π interactions with a pyridine ring. These nonclassical hydrogen bonds extend the molecule into a three‐dimensional network.     

Four N7‐alkoxybenzyl‐substituted 4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐diones: hydrogen‐bonded supramolecular structures in zero,one, two or three dimensions

3‐tert‐Butyl‐7‐(4‐methoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₇N₃O₃, (I), 3‐tert‐butyl‐7‐(2,3‐dimethoxybenzyl)‐4′,4′‐dimethyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₂H₃₉N₃O₄, (II), 3‐tert‐butyl‐4′,4′‐dimethyl‐7‐(3,4‐methylenedioxybenzyl)‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione, C₃₁H₃₅N₃O₄, (III), and 3‐tert‐butyl‐4′,4′‐dimethyl‐1‐phenyl‐7‐(3,4,5‐trimethoxybenzyl)‐4,5,6,7‐tetrahydro‐1H‐pyrazolo[3,4‐b]pyridine‐5‐spiro‐1′‐cyclohexane‐2′,6′‐dione ethanol 0.67‐solvate, C₃₃H₄₁N₃O₅·0.67C₂H₆O, (IV), all contain reduced pyridine rings having half‐chair conformations. The molecules of (I) and (II) are linked into centrosymmetric dimers and simple chains, respectively, by C—H...O hydrogen bonds, augmented only in (I) by a C—H...π hydrogen bond. The molecules of (III) are linked by a combination of C—H...O and C—H...π hydrogen bonds into a chain of edge‐fused centrosymmetric rings, further linked by weak hydrogen bonds into supramolecular arrays in two or three dimensions. The heterocyclic molecules in (IV) are linked by two independent C—H...O hydrogen bonds into sheets, from which the partial‐occupancy ethanol molecules are pendent. The significance of this study lies in its finding of a very wide range of supramolecular aggregation modes dependent on rather modest changes in the peripheral substituents remote from the main hydrogen‐bond acceptor sites.     

Unconventional hydrogen bonding and π‐stacking in two substituted pyridine carboxamides

The crystal structures of two para‐substituted aryl derivatives of pyridine‐2‐carboxamide, namely N‐(4‐fluorophenyl)pyridine‐2‐carboxamide, C₁₂H₉FN₂O, (I), and N‐(4‐nitrophenyl)pyridine‐2‐carboxamide, C₁₂H₉N₃O₃, (II), have been studied. Compound (I) exhibits unconventional aryl–carbonyl C—H...O and pyridine–fluorine C—H...F hydrogen bonding in two dimensions and well defined π‐stacking involving pyridine rings in the third dimension. The conformation of (II) is more nearly planar than that of (I) and the intermolecular interactions comprise one‐dimensional aryl–carbonyl C—H...O hydrogen bonds leading to a stepped or staircase‐like progression of loosely π‐stacked molecules. The close‐packed layers of planar π‐stacked molecules are related by inversion symmetry. Two alternating interplanar separations of 3.439 (1) and 3.476 (1) Å are observed in the crystal lattice and are consistent with a repetitive packing sequence, ABA′B′AB…, for the π‐stacked inversion pairs of (II).     

catena‐Poly[[(trifluoro­methane­sulfon­ato‐κO)silver(I)]‐μ‐di‐2‐pyridyl­amine‐κ2N2:N2′], a chain polymer with short Ag⋯C contacts

The title compound, [Ag(CF₃O₃S)(C₁₀H₉N₃)]_n, is a chain polymer in which neighbouring monomeric units are related by a glide plane. The silver centre is four‐coordinate; the donor atoms are one trifluoro­methane­sulfonate O atom and one pyridine N atom from each of two symmetry‐related dipyridylamines, and an additional and unexpected Ag⋯C contact [2.6464 (16) Å] is observed to a pyridine C atom. The chains are reinforced by one classical N—H⋯O and two `weak' C—H⋯O hydrogen bonds.     

Anomeric Stereoauxiliary Cleavage of the C−N Bond of d-Glucosamine for the Preparation of Imidazo[1,5-a]pyridines

The targeted cleavage of the C−N bonds of alkyl primary amines in sustainable compounds of biomass according to a metal-free pathway and the conjunction of nitrogen in the synthesis of imidazo[1,5-a]pyridines are still highly challenging. Despite tremendous progress in the synthesis of imidazo[1,5-a]pyridines over the past decade, many of them can still not be efficiently prepared. Herein, we report an anomeric stereoauxiliary approach for the synthesis of a wide range of imidazo[1,5-a]pyridines after cleaving the C−N bond of d -glucosamine (α-2° amine) from biobased resources. This new approach expands the scope of readily accessible imidazo[1,5-a]pyridines relative to existing state-of-the-art methods. A key strategic advantage of this approach is that the α-anomer of d -glucosamine enables C−N bond cleavage via a seven-membered ring transition state. By using this novel method, a series of imidazo[1,5-a]pyridine derivatives (>80 examples) was synthesized from pyridine ketones (including para-dipyridine ketone) and aldehydes (including para-dialdehyde). Imidazo[1,5-a]pyridine derivatives containing diverse important deuterated C(sp²)−H and C(sp³)−H bonds were also efficiently achieved.     

A bromine analogue of picoplatin: a new substance from the group of platinum‐based chemotherapeutics

A new substance, cis‐amminedibromido(2‐methylpyridine‐κN)platinum(II), cis‐[PtBr₂(C₆H₇N)(NH₃)], which is a potential platinum‐based antineoplastic agent for the treatment of patients with solid tumors, has been synthesized and structurally characterized. There is one molecule in the asymmetric unit and molecules are linked via two symmetry‐independent N—H...Br hydrogen bonds into zigzag chains running parallel to the c axis. C—H...Br hydrogen bonds crosslink these chains to give a layer parallel to (010). N—H...Br hydrogen bonds and π–π stacking interactions between pairs of pyridine rings stack the layers along b.     

Mixed Directing‐Group Strategy: Oxidative C−H/C−H Bond Arylation of Unactivated Arenes by Cobalt Catalysis

A mixed directing‐group strategy for inexpensive [Co(acac)₃]‐catalyzed oxidative C?H/C?H bond arylation of unactivated arenes has been disclosed. This strategy enables the arylation of a wide range of benzamide and arylpyridines effectively to afford novel bifunctionalized biaryls, which are difficult to achieve by common synthetic routes. Two different pathways, namely, a single‐electron‐transmetalation process (8‐aminoquinoline‐directed) and a concerted metalation–deprotonation process (pyridine‐directed), were involved to activate two different inert aromatic C?H bonds. Moreover, the aryl radicals have been trapped by 2,6‐di‐tert‐butyl‐4‐methylphenol to form benzylated products. This unique strategy should be useful in the design of other arene C?H/C?H cross‐couplings as well.     

trans‐Dichloro(dimethyl sulfide‐κS)(pyridine‐κN)platinum(II)

The structure of the title compound, [PtCl₂(C₅H₅N)(C₂H₆S)], consists of discrete mol­ecules in which the Pt‐atom coordination is slightly distorted square planar. The Cl atoms are trans to each other, with a Cl—Pt—Cl angle of 176.60 (7)°. The pyridine ligand is rotated 64.5 (2)° from the Pt square plane and one of the Pt—Cl bonds essentially bisects the C—S—C angle of the di­methyl sulfide ligand. In the crystal structure, there are extensive weak C—H⋯Cl interactions, the shortest of which connects mol­ecules into centrosymmetric dimers. A comparison of the structural trans influence on Pt—S and Pt—­N distances for PtS(CH₃)₂ and Pt(pyridine) fragments, respectively, in square‐planar Pt^II complexes is presented.     

Hydro­gen‐bond networks in tris(4‐hydroxy­phenyl)­methane and its 1:1 molecular complex with 4,4′‐bi­pyridine

In tris(4‐hydroxy­phenyl)­methane (or 4,4′,4′′‐methane­triyl­tri­phenol), C₁₉H₁₆O₃, mol­ecules are connected by O—H⃛O hydrogen bonds [O⃛O = 2.662 (2) and 2.648 (2) Å] into two‐dimensional square networks that are twofold interpenetrated. In tris(4‐hydroxy­phenyl)­methane–4,4′‐bi­pyridine (1/1), C₁₉H₁₆O₃·C₁₀H₈N₂, trisphenol mol­ecules form rectangular networks via O—H⃛O [O⃛O = 2.694 (3) Å] and C—H⃛O [C⃛O = 3.384 (3) Å] hydrogen bonds. Bi­pyridine mol­ecules hydrogen bonded to phenol moieties [O⃛N = 2.622 (3) and 2.764 (3) Å] fill the voids to complete the structure.     

2‐Amino‐5‐methyl­pyridinium (2‐amino‐5‐methyl­pyridine)trichloro­zincate(II)

The title compound, (C₆H₉N₂)[ZnCl₃(C₆H₈N₂)], consists of one 2‐amino‐5‐methyl­pyridinium cation and one (2‐amino‐5‐methyl­pyridine)trichloro­zincate(II) anion, which are held together by N—H·Cl hydrogen bonds and π–π inter­actions. The cation and the pyridine ligand show similar geometric features, except for the N—C bond lengths. Mol­ecules of the title compound are connected by N—H·Cl hydrogen bonds to form chiral chains; these chains are associated further by C—H·Cl hydrogen bonds to form layers, which are in turn linked by π–π inter­actions.