4‐Hydroxy‐7‐methoxy‐2‐methyl‐5H‐1‐benzopyrano[4,3‐b]pyridin‐5‐one

The title compound, C₁₄H₁₁NO₄, consists of a methoxy‐substituted coumarin skeleton fused to a 2‐methyl‐4‐pyridone ring. The ring system of the mol­ecule is approximately planar and the methoxy group is roughly coplanar with the ring plane. The 4‐pyridone ring exists in a 4‐hydroxy tautomeric form and is stabilized by an intramolecular hydrogen bond between the O—H and C=O groups. Comparison of the results with those found for other structures containing the 4‐pyridone substructure reveals a substantial effect of the nature of the substituents bonded to the pyridine ring on the keto–enol tautomerism.     

A simple compound with an ­unexpectedly complex structure: 4‐pyridone 6/5‐hydrate

The crystal structure of the title compound, C₅H₅NO·H₂O, contains five independent mol­ecules of pyridone and six independent water mol­ecules. The space group is P2₁, but four of the pyridones and four waters correspond closely to P2₁/n. The packing involves two layers; one consists of head‐to‐tail chains of pyridone mol­ecules 1–4 linked by N—H?O hydrogen bonds, and a second layer involves all the waters and the fifth pyridone. The layers are linked by hydrogen bonds from water to pyridone oxy­gen. The four water O atoms that accept only one classical hydrogen bond have their environment completed by C—H?O interactions.     

Channel‐forming solvate crystals and isostructural solvent‐free powder of 5‐hydroxy‐6‐methyl‐2‐pyridone

Crystals of 5‐hydroxy‐6‐methyl‐2‐pyridone, (I), grown from a variety of solvents, are invariably trigonal (space group R); these are 5‐hydroxy‐6‐methyl‐2‐pyridone acetone 0.1667‐solvate, C₆H₇NO₂·0.1667C₃H₆O, (Ia), and 6‐methyl‐5‐hydroxy‐2‐pyridone propan‐2‐ol 0.1667‐solvate, C₆H₇NO₂·0.1667C₃H₈O, (Ib), and the forms from methanol, (Ic), water, (Id), benzonitrile, (Ie), and benzyl alcohol, (If). They incorporate channels running the length of the c axis that contain extensively disordered solvent molecules. A solvent‐free sublimed powder of 5‐hydroxy‐6‐methyl‐2‐pyridone microcrystals is essentially isostructural. Inversion‐related host molecules interact via pairs of N—H...O hydrogen bonds to form R₂²(8) dimers. Six of these dimers form large R₁₂⁶(42) puckered rings, in which the O atom of each N—H...O hydrogen bond is also the acceptor in an O—H...O hydrogen bond that involves the 5‐hydroxy group. The large R₁₂⁶(42) rings straddle the axes and form stacked columns viaπ–π interactions between inversion‐related molecules of (I) [mean interplanar spacing = 3.254 Å and ring centroid–centroid distance = 3.688 (2) Å]. The channels are lined by methyl groups, which all point inwards to the centre of the channels.     

A study of the planarity of the pyrrolone fragment in 2‐isopropyl‐2,3‐dihydro‐1H‐isoindol‐1‐one

Orthophthalaldehyde (o‐phthalaldehyde, OPA) is an aromatic dialdehyde bearing two electron‐withdrawing carbonyl groups. The reactions of OPA with primary amines are broadly applied for the synthesis of important heterocyclic compounds with biological relevance. A number of such reactions have been investigated recently and several structures of condensation products have been reported, however, the complex reaction mechanism is still not fully understood and comprises concurrent as well as consecutive reactions. The reaction products depend on the primary amine which reacts with OPA, the reaction environment (solvent) and the proportion of the reactants. The title molecule, C₁₁H₁₃NO, the product of the reaction of OPA with isopropylamine, contains a five‐membered pyrrole C₄N ring with a carbonyl substituent, which forms part of the isoindolinone unit. Though this pyrrole ring contains one C atom in the sp³‐hybridized state, it is fairly planar. The title molecule has been compared with similar structures retrieved from the Cambridge Structural Database in order to study this phenomenon. The planarity of this fragment has been explained by the presence of partially delocalized C—C, C—N and C—O bonds, and by an inner angle in the planar pentagonal ring (∼108°), which is close to the ideal tetrahedral value for the sp³‐hybridized state of the constituent C atom. Due to this propitious angle, this C atom can be present in states intermediate between sp³‐ and sp²‐hybridized in different structures, while still maintaining the planarity of the ring. There are only weak intermolecular C—H…O hydrogen bonds and C—H…π‐electron ring interactions in the structure. In particular, it is the pyrrole ring which is involved in these interactions.     

4‐Ethynyl‐4‐hydroxycyclohexan‐1‐one and 4‐ethynyl‐4‐hydroxy‐2,3,5,6‐tetramethylcyclohexa‐2,5‐dien‐1‐one

The title compounds, C₈H₁₀O₂, (I), and C₁₂H₁₄O₂, (II), occurred as by‐products in the controlled synthesis of a series of bis­(gem‐alkynols), prepared as part of an extensive study of synthon formation in simple gem‐alkynol derivatives. The two 4‐(gem‐alkynol)‐1‐ones crystallize in space group P2₁/c, (I) with Z′ = 1 and (II) with Z′ = 2. Both structures are dominated by O—H?O=C hydrogen bonds, which form simple chains in the cyclo­hexane derivative, (I), and centrosymmetric dimers, of both symmetry‐independent mol­ecules, in the cyclo­hexa‐2,5‐diene, (II). These strong synthons are further stabilized by C[triple‐bond]C—H?O=C, C_methylene—H?O(H) and C_methyl—H?O(H) interactions. The direct intermolecular interactions between donors and acceptors in the gem‐alkynol group, which characterize the bis­(gem‐alkynol) analogues of (I) and (II), are not present in the ketone derivatives studied here.     

Asymmetric α‐Hydroxylation of a Lactone with Vinylogous Pyridone by Using a Guanidine–Urea Bifunctional Organocatalyst: Catalytic Enantioselective Synthesis of a Key Intermediate for (20S)‐Camptothecin Analogues

We have developed a catalytic asymmetric synthesis of (S)‐4‐ethyl‐6,6‐(ethylenedioxy)‐7,8‐dihydro‐4‐hydroxy‐1H‐pyrano[3,4‐f]indolizine‐3,10(4H)dione ( 5 a ), a synthetic intermediate for (20S)‐camptothecin analogues. A key step in this synthesis is an asymmetric α‐hydroxylation of a lactone with a vinylogous pyridone structure ( 8 a ) by using a guanidine–urea bifunctional organocatalyst. The present oxidation was successfully applied to the synthesis of C20‐modified derivatives of (+)‐C20‐desethylbenzylcamptothecin ( 13 ).     

One‐Pot Synthesis of 4‐Aryl‐NH‐1,2,3‐Triazoles through Three‐Component Reaction of Aldehydes,Nitroalkanes and NaN3

A one‐pot three‐component reaction of aldehydes, nitroalkanes and NaN₃ for the synthesis of NH ‐1,2,3‐triazoles has been developed. The reaction provides a safe, efficient and step‐economic approach for the synthesis of various NH ‐1,2,3‐triazoles in good to excellent yields.     

6β‐Hydroxy‐5β‐methyl‐20‐oxo‐19‐norpregn‐9(10)‐en‐3β‐yl acetate

In the title compound, C₂₃H₃₄O₄, which is an intermediate in the synthesis of pregnane derivatives with a modified skeleton that show potent abortion‐inducing activity, the conformation of ring B is close to half‐chair due to the presence of both the C=C double bond and the axial 5β‐methyl group. Rings A and C have conformations close to chair, while ring D has a twisted conformation around the bridgehead C—C bond. Molecules are hydrogen bonded via the hydroxyl and acetoxy groups into infinite chains. Quantum‐mechanical ab initio Roothan Hartree–Fock calculations show that crystal packing might be responsible for the low values of the angles between rings A and B, and between ring A and rings C and D, as well as for a different steric position of the methyl ketone side chain compared to the geometry of the free molecule.     

4,4′‐Bis(2,2,2‐trifluoroethoxymethyl)‐2,2′‐bipyridine

As part of a homologous series of novel polyfluorinated bipyridyl (bpy) ligands, the title compound, C₁₆H₁₄F₆N₂O₂, contains the smallest fluorinated group, viz. CF₃. The molecule resides on a crystallographic inversion centre at the mid‐point of the pyridine C_ipso—C_ipso bond. Therefore, the bpy skeleton lies in an anti conformation to avoid repulsion between the two pyridyl N atoms. Weak intramolecular C—H...N and C—H...O interactions are observed, similar to those in related polyfluorinated bpy–metal complexes. A π–π interaction is observed between the bpy rings of adjacent molecules and this is probably a primary driving force in crystallization. Weak intermolecular C—H...N hydrogen bonding is present between one of the CF₃CH₂– methylene H atoms and a pyridyl N atom related by translation along the [010] direction, in addition to weak benzyl‐type C—H...F interactions to atoms of the terminal CF₃ group. It is of note that the O—CH₂CF₃ bond is almost perpendicular to the bpy plane.     

{5′‐O‐[Bis(4‐methoxyphenyl)(phenyl)methyl]‐2′‐deoxy‐β‐D‐threopentofuranosyl}thymine ethyl acetate 0.25‐solvate

The title compound, C₃₁H₃₂N₂O₇·0.25C₄H₈O₂, is a key intermediate in the synthesis of [¹⁸F]fluorine‐labelled thymidine (¹⁸F‐FLT), which is the most widely used molecular imaging probe for positron emission tomography (PET). The crystallographic asymmetric unit contains two independent thymine molecules plus one partially occupied site for an ethyl acetate molecule. The two independent thymine molecules show similar geometrical features, except that the dimethoxytrityl groups adopt different orientations with respect to the remainder of the molecule. Each thymine base adopts an anti conformation with respect to the attached deoxyribose ring, and the deoxyribose rings show C3‐endo puckering. The conformation of the side chain at the C1 position of the deoxyribose ring is gauche+. Intermolecular N—H...O and O—H...O hydrogen bonds link the molecules into one‐dimensional chains.     

Hydrogen‐bonded bilayers in 7‐benzyl‐3‐tert‐butyl‐1‐phenyl‐4,5,6,7‐tetrahydro‐1H‐spiro[pyrazolo[3,4‐b]pyridine‐5,2′‐indan]‐1′,3′‐dione

In the title compound, C₃₁H₂₉N₃O₂, the reduced pyridine ring adopts a conformation intermediate between the envelope and half‐chair forms. The aryl rings of the benzyl and phenyl substituents are nearly parallel and overlap, indicative of an intramolecular π–π stacking interaction. A combination of two C—H...O hydrogen bonds and one C—H...N hydrogen bond links the molecules into a bilayer having tert‐butyl groups on both faces.<!?tpb=19.5pt>     

Three different fluoro‐ or chloro‐substituted 1′‐deoxy‐1′‐phenyl‐β‐D‐ribofuranoses

Crystal structures are reported for three fluoro‐ or chloro‐substituted 1′‐deoxy‐1′‐phenyl‐β‐D‐ribofuranoses, namely 1′‐deoxy‐1′‐(2,4,5‐trifluorophenyl)‐β‐D‐ribofuranose, C₁₁H₁₁F₃O₄, (I), 1′‐deoxy‐1′‐(2,4,6‐trifluorophenyl)‐β‐D‐ribofuranose, C₁₁H₁₁F₃O₄, (II), and 1′‐(4‐chlorophenyl)‐1′‐deoxy‐β‐D‐ribofuranose, C₁₁H₁₃ClO₄, (III). The five‐membered furanose ring of the three compounds has a conformation between a C2′‐endo,C3′‐exo twist and a C2′‐endo envelope. The ribofuranose groups of (I) and (III) are connected by intermolecular O—H...O hydrogen bonds to six symmetry‐related molecules to form double layers, while the ribofuranose group of (II) is connected by O—H...O hydrogen bonds to four symmetry‐related molecules to form single layers. The O...O contact distance of the O—H...O hydrogen bonds ranges from 2.7172 (15) to 2.8895 (19) Å. Neighbouring double layers of (I) are connected by a very weak intermolecular C—F...π contact. The layers of (II) are connected by one C—H...O and two C—H...F contacts, while the double layers of (III) are connected by a C—H...Cl contact. The conformations of the molecules are compared with those of seven related molecules. The orientation of the benzene ring is coplanar with the H—C1′ bond or bisecting the H—C1′—C2′ angle, or intermediate between these positions. The orientation of the benzene ring is independent of the substitution pattern of the ring and depends mainly on crystal‐packing effects.     

Two polymorphs of anhydrous 4‐pyridone at 100 K

Two polymorphs of the title compound, C₅H₅NO, (I), have been obtained from ethanol. One polymorph crystallizes in the monoclinic space group C2/c [henceforth (I)‐M], while the other crystallizes in the orthorhombic space group Pbca [henceforth (I)‐O]. In the two forms, the lattice parameters, cell volume and packing motifs are very similar. There are also two independent molecules of 4‐pyridone in each asymmetric unit. The molecules are linked by N—H...O hydrogen bonds into one‐dimensional zigzag chains extending along the b axis in the (I)‐M polymorph and along the a axis in the (I)‐O polymorph, with the graph set C₂²(12). The structures are stabilized by weak C—H...O hydrogen bonds linking adjacent chains, thus forming a ring with the graph set R₆⁵(28). The significance of this study lies in the analysis of the hydrogen‐bond interactions occurring in these structures. Analyses of the crystal structures of the two polymorphs of 4‐pyridone are helpful in elucidating the mechanism of the generation of spectroscopic effects observed in the IR spectra of these polymorphs in the frequency range of the N—H stretching vibration band.     

Channel‐forming solvates of 6‐chloro‐2,5‐dihydroxypyridine and its solvent‐free tautomer 6‐chloro‐5‐hydroxy‐2‐pyridone

On crystallization from CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂, 6‐chloro‐5‐hydroxy‐2‐pyridone, C₅H₄ClNO₂, (I), undergoes a tautomeric rearrangement to 6‐chloro‐2,5‐dihydroxypyridine, (II). The resulting crystals, viz. 6‐chloro‐2,5‐dihydroxypyridine chloroform 0.125‐solvate, C₅H₄ClNO₂·0.125CHCl₃, (IIa), 6‐chloro‐2,5‐dihydroxypyridine carbon tetrachloride 0.125‐solvate, C₅H₄ClNO₂.·0.125CCl₄, (IIb), 6‐chloro‐2,5‐dihydroxypyridine 1,2‐dichloroethane solvate, C₅H₄ClNO₂·C₂H₄Cl₂, (IIc), and 6‐chloro‐2,5‐dihydroxypyridine 1,1,2,2‐tetrachloroethane solvate, C₅H₄ClNO₂·C₂H₂Cl₄, (IId), have I4₁/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent‐free crystals with P2₁/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion‐related molecules form R²₂(8) dimers via pairs of N—H...O hydrogen bonds. The dimers are linked by O—H...O hydrogen bonds into R⁴₆(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel‐containing pyridine solvate crystals, viz. (IIa)–(IId), two independent host molecules form an R²₂(8) dimer via a pair of O—H...N hydrogen bonds. One molecule is further linked by O—H...O hydrogen bonds to two 4₁ screw‐related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O—H...O hydrogen bonded to two related equivalents to form tetrameric R⁴₄(28) rings. The dimers are π–π stacked with inversion‐related dimers, which in turn stack the R⁴₄(28) rings along c to form continuous solvent‐accessible channels. CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂ solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels.     

3,17‐Dioxoandrost‐4‐en‐4‐yl acetate

The title compound, C₂₁H₂₈O₄, has a 4‐acetoxy substituent positioned on the steroid α face. The six‐membered ring A assumes a conformation intermediate between 1α,2β‐half chair and 1α‐sofa. A long Csp³—Csp³ bond is observed in ring B and reproduced in quantum‐mechanical ab initio calculations of the isolated molecule using a molecular‐orbital Hartree–Fock method. Cohesion of the crystal can be attributed to van der Waals interactions and weak C—H...O hydrogen bonds.     

1,2:1,3‐Bis(μ‐p‐toluato‐O:O′)‐1‐(triphenylphosphine‐P)‐1‐ruthena‐closo‐undecaborane

The title compound, [(PPh₃)(p‐MeC₆H₄COO)₂RuB₁₀H₈], contains an 11‐vertex closo‐type RuB₁₀ cluster fused to two symmetric exo­poly­hedral Ru—O—C—O—B five‐membered rings. Principal distances include Ru—B 2.010 (5)–2.392 (4) Å and Ru—O 2.218 (5) and 2.222 (2) Å.     

Rhodium‐catalyzed ortho‐C‐H olefination of aromatic aldehydes employing transient directing strategy

A Rhodium(III)‐catalyzed ortho‐C‐H olefination of aromatic aldehydes in the presence of catalytic amount of TsNH₂ has been developed. The in situ generated imine intermediate from aldehyde and TsNH₂ worked as a transient directing group. Both electron‐rich and electron‐deficient aromatic aldehydes were tolerated, affording the corresponding products in moderate to good yields. Importantly, the present protocol provides a straightforward access to olefinated aromatic aldehydes with aldehydes as the simple starting materials.     

2‐Pyridone–tartronic acid (1/1), 3‐hydroxy­pyridinium hydrogen tartronate and 4‐hydroxy­pyridinium hydrogen tartronate

Tartronic acid forms a hydrogen‐bonded complex, C₅H₅NO·C₃H₄O₅, (I), with 2‐pyridone, while it forms acid salts, namely 3‐hydroxy­pyridinium hydrogen tartronate, (II), and 4‐hy­droxy­pyridinium hydrogen tartronate, (III), both C₅H₆NO⁺·C₃H₃O₅⁻, with 3‐hydroxy­pyridine and 4‐hydroxy­pyridine, respectively. In (I), the pyridone mol­ecules and the acid mol­ecules form R(8) and R(10) hydrogen‐bonded rings, respectively, around the inversion centres. In (II) and (III), the cations and anions are linked by N—H⋯O and O—H⋯O hydrogen bonds to form a hydrogen‐bonded chain. In each of (I), (II) and (III), an intermolecular hydrogen bond is formed between a carboxyl group and the hydroxyl group attached to the central C atom, and in (I), the hydroxyl group participates in an intramolecular hydrogen bond with a carbonyl group. No intermolecular hydrogen bond is formed between the carboxyl groups in (I), or between the carboxyl and carboxyl­ate groups in (II) and (III).     

Methyl 2‐benzamido‐4‐(3,4‐dimethoxyphenyl)‐5‐methylbenzoate and N‐{5‐benzoyl‐2‐[(Z)‐2‐methoxyethenyl]‐4‐methylphenyl}benzamide

Methyl 2‐benzamido‐4‐(3,4‐dimethoxyphenyl)‐5‐methylbenzoate, C₂₄H₂₃NO₅, (Ia), and N‐{5‐benzoyl‐2‐[(Z)‐2‐methoxyethenyl]‐4‐methylphenyl}benzamide, C₂₄H₂₁NO₃, (IIa), were formed via a Diels–Alder reaction of appropriately substituted 2H‐pyran‐2‐ones and methyl propiolate or (Z)‐1‐methoxybut‐1‐en‐3‐yne, respectively. Each of these cycloadditions might yield two different regioisomers, but just one was obtained in each case. In (Ia), an intramolecular N—H...O hydrogen bond closes a six‐membered ring. A chain is formed due to aromatic π–π interactions, and a three‐dimensional framework structure is formed by a combination of C—H...O and C—H...π(arene) hydrogen bonds. Compound (IIa) was formed not only regioselectively but also chemoselectively, with just the triple bond reacting and the double bond remaining unchanged. Compound (IIa) crystallizes as N—H...O hydrogen‐bonded dimers stabilized by aromatic π–π interactions. Dimers of (IIa) are connected into a chain by weak C—H...π(arene) interactions.     

A low‐temperature modification of hexa‐tert‐butyldisilane and a new polymorph of 1,1,2,2‐tetra‐tert‐butyl‐1,2‐diphenyldisilane

Crystals of hexa‐tert‐butyldisilane, C₂₄H₅₄Si₂, undergo a reversible phase transition at 179 (2) K. The space group changes from Ibca (high temperature) to Pbca (low temperature), but the lattice constants a, b and c do not change significantly during the phase transition. The crystallographic twofold axis of the molecule in the high‐temperature phase is replaced by a noncrystallographic twofold axis in the low‐temperature phase. The angle between the two axes is 2.36 (4)°. The centre of the molecule undergoes a translation of 0.123 (1) Å during the phase transition, but the conformation angles of the molecule remain unchanged. Between the two tri‐tert‐butylsilyl subunits there are six short repulsive intramolecular C—H...H—C contacts, with H...H distances between 2.02 and 2.04 Å, resulting in a significant lengthening of the Si—Si and Si—C bonds. The Si—Si bond length is 2.6863 (5) Å and the Si—C bond lengths are between 1.9860 (14) and 1.9933 (14) Å. Torsion angles about the Si—Si and Si—C bonds deviate by approximately 15° from the values expected for staggered conformations due to intramolecular steric H...H repulsions. A new polymorph is reported for the crystal structure of 1,1,2,2‐tetra‐tert‐butyl‐1,2‐diphenyldisilane, C₂₈H₄₆Si₂. It has two independent molecules with rather similar conformations. The Si—Si bond lengths are 2.4869 (8) and 2.4944 (8) Å. The C—Si—Si—C torsion angles deviate by between −3.4 (1) and −18.5 (1)° from the values expected for a staggered conformation. These deviations result from steric interactions. Four Si—C(t‐Bu) bonds are almost staggered, while the other four Si—C(t‐Bu) bonds are intermediate between a staggered and an eclipsed conformation. The latter Si—C(t‐Bu) bonds are about 0.019 (2) Å longer than the staggered Si—C(t‐Bu) bonds.