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.     

Reactions of 2‐amino‐4h‐1‐benzopyran‐4‐one with 4‐oxo‐4h‐1‐benzopyran‐3‐carbaldehydes

The title aldehyde 1 reacts smoothly with the enamine moiety of 2 ‐aminochromone 2 to produce hitherto unreported 3‐(2‐hydroxybenzoyl)‐5H‐1‐benzopyrano[2,3‐b]pyridin‐5‐one (azaxanthone) 5 . This reaction has been extended for the synthesis of bisazaxanthone 9.     

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.     

Three polymorphs of 4‐4′‐diiodobenzalazine,and 4‐chloro‐4′‐iodobenzalazine

Three polymorphs of 4,4′‐diiodobenzalazine (systematic name: 4‐iodobenzaldehyde azine), C₁₄H₁₀I₂N₂, have crystallographically imposed inversion symmetry. 4‐Chloro‐4′‐iodobenzalazine [systematic name: 1‐(4‐chlorobenzylidene)‐2‐(4‐iodobenzylidene)diazane], C₁₄H₁₀ClIN₂, has a partially disordered pseudocentrosymmetric packing and is not isostructural with any of the polymorphs of 4,4′‐diiodobenzalazine. All structures pack utilizing halogen–halogen interactions; some also have weak π (benzene ring) interactions. A comparison with previously published methylphenylketalazines (which differ by substitution of methyl for H at the azine C atoms) shows a fundamentally different geometry for these two classes, namely planar for the alazines and twisted for the ketalazines. Density functional theory calculations confirm that the difference is fundamental and not an artifact of packing forces.     

4‐Aminopyridinium 4‐aminobenzoate dihydrate and 4‐aminopyridinium nicotinate

In the title compounds, 4‐aminopyridinium 4‐aminobenzoate dihydrate, C₇H₆NO₂⁻·C₅H₇N₂⁺·2H₂O, (I), and 4‐aminopyridinium nicotinate, C₅H₇N₂⁺·C₆H₄NO₂⁻, (II), the aromatic N atoms of the 4‐aminopyridinium cations are protonated. In (I), the asymmetric unit is composed of two 4‐aminopyridinium cations, two 4‐aminobenzoate anions and four water molecules, and the compound crystallizes in a noncentrosymmetric space group. The two sets of independent molecules of (I) are related by a centre of symmetry which is not part of the space group. In (I), the protonated pyridinium ring H atoms are involved in bifurcated hydrogen bonding with carboxylate O atoms to form an R₁²(4) ring motif. The water molecules link the ions to form a two‐dimensional network along the (10) plane. In (II), an intramolecular bifurcated hydrogen bond generates an R₁²(4) ring motif and inter‐ion hydrogen bonding generates an R₄²(16) ring motif. The packing of adduct (II) is consolidated via N—H...O and N—H...N hydrogen bonds to form a two‐dimensional network along the (10) plane.     

4‐Deoxy‐4‐fluoro‐β‐d‐glucopyranose

4‐Deoxy‐4‐fluoro‐β‐d ‐glucopyranose, C₆H₁₁FO₅, (I), crystallizes from water at room temperature in a slightly distorted ⁴C₁ chair conformation. The observed chair distortion differs from that observed in β‐d ‐glucopyranose [Kouwijzer, van Eijck, Kooijman & Kroon (1995). Acta Cryst. B 51 , 209–220], (II), with the former skewed toward a B^C3,O5 (boat) conformer and the latter toward an ^O5TB_C2 (twist–boat) conformer, based on Cremer–Pople analysis. The exocyclic hydroxymethyl group conformations in (I) and (II) are similar; in both cases, the O—C—C—O torsion angle is ∼−60° (gg conformer). Intermolecular hydrogen bonding in the crystal structures of (I) and (II) is conserved in that identical patterns of donors and acceptors are observed for the exocyclic substituents and the ring O atom of each monosaccharide. Inspection of the crystal packing structures of (I) and (II) reveals an essentially identical packing configuration.     

A mechanistic approach to photochemical behavior of 4‐anisyl‐4‐methyl‐2,6‐diphenyl‐4H‐thiopyran‐1,1‐dioxide

Photoisomerization of 4‐anisyl‐4‐methyl‐2,6‐diphenyl‐4H‐thiopyran‐1,1‐dioxide is described in the presence of a sensitizer and new mechanistic features are proposed. The relative molar ratios of the stereoselective photoproducts compared in the presence and the absence of sensitizer in different concentrations of the starting material using hplc. The results observed are discussed on the basis of a triplet excited state thiadi‐π‐methane rearrangement.     

4‐(4‐Hydro­xy­benzyl­idene­amino)‐4H‐1,2,4‐triazole hemihydrate

In the title compound, 4‐(4H‐1,2,4‐triazol‐4‐yl­imino­methyl)­phenol hemi­hydrate, C₉H₈N₄O·0.5H₂O or (I)·0.5H₂O, mol­ecules of (I) are arranged as layers running along the b axis through intermolecular O—H?N and C—H?O hydrogen bonds. These layers are stabilized by hydrogen‐bonded water mol­ecules to form three‐dimensional networks.     

Decarboxylation in the synthesis of 4‐alkyl‐, 4‐alkenyl‐ and 4‐acylpyrimidines

Decarboxylation of allylic esters of 4‐carboxypyrimidines in toluene at 111 °C in the presence of a Pd(0) catalyst, gives a mixture of a 4‐alkenylpyrimidine and a pyrimidine unsubstituted in the 4‐position. If the decarboxylation is carried out in the presence of benzaldehyde, then benzaldehyde is added to the 4‐position. Decarboxylation of 4‐carboxypyrimidines in the presence of different electrophiles, results in incorporation of the electrophile into the 4‐position together with a pyrimidine unsubstituted in the 4‐position. Use of microwave irradiation enhances the rate of the decarboxylations.     

2‐Amino‐4‐(4‐chlorophenyl)‐7,7‐dimethyl‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitrile

The supramolecular structure of the title compound, C₁₈H₁₇ClN₂O₂, is determined by the intersection of two chains formed by N—H⋯O and N—H⋯N hydrogen bonds, forming a two‐dimensional sheet.     

4‐(4‐Chloro­phen­yl)‐3‐(4‐phenyl­pent‐4‐en­yloxy)‐1,3‐thia­zole‐2(3H)‐thione

The title compound, C₂₀H₁₈ClNOS₂, is a thia­zole‐derived thio­hydroxamic acid O‐ester. The value of Z′ is 3 and the asymmetric unit comprises three mol­ecules of identical helicity along the N—O bond. Two of these show an anti and the third a syn arrangement of substituents attached in positions 3 and 4 to the 1,3‐thia­zole nucleus.     

5‐Acetyl‐2‐amino‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile and 2‐amino‐5‐benzoyl‐6‐methyl‐4‐phenyl‐4H‐pyran‐3‐carbonitrile acetonitrile solvate

The syntheses, X‐ray structural investigations and calculations of the conformational preferences of the carbonyl substituent with respect to the pyran ring have been carried out for the two title compounds, viz. C₁₅H₁₄N₂O₂, (II), and C₂₀H₁₆N₂O₂·C₂H₃N, (III), respectively. In both mol­ecules, the heterocyclic ring adopts a flattened boat conformation. In (II), the carbonyl group and a double bond of the heterocyclic ring are syn, but in (III) they are anti. The carbonyl group forms a short contact with a methyl group H atom in (II). The dihedral angles between the pseudo‐axial phenyl substituent and the flat part of the pyran ring are 92.7 (1) and 93.2 (1)° in (II) and (III), respectively. In the crystal structure of (II), inter­molecular N—H⋯N and N—H⋯O hydrogen bonds link the mol­ecules into a sheet along the (103) plane, while in (III), they link the mol­ecules into ribbons along the a axis.     

The Photocyclodimers of 2,3‐Dihydro‐2,2‐dimethyl‐4H‐pyran‐4‐one

On irradiation (350 nm) in benzene solution, dihydropyranone 3 affords predominantly (75%) the cis‐anti‐cis HH‐dimer 4 , but in smaller amounts (12%) also dimer 5 , wherein one of the six‐membered rings is trans‐fused to the (central) cyclobutane ring. The constitution and configuration of 5 was fully elucidated by NMR‐analysis. On contact with SiO₂, 5 isomerizes quantitatively to the cis‐anti‐cis HT‐dimer 7 , the structure of which was established by X‐ray crystal‐structure determination.     

Reactivity of 2‐Methyl‐4H‐3,1‐benzoxazin‐4‐ones and 2‐Methyl‐4H‐pyrido[2,3‐d][1,3]oxazin‐4‐one under Microwave Irradiation Conditions

The reactivity of variably substituted 2‐methyl‐4H‐3,1‐benzoxazin‐4‐ones and 2‐methyl‐4H‐pyrido[2,3‐d][1,3]oxazin‐4‐one towards carbon and oxygen nucleophiles under microwave irradiation conditions was investigated. Optimization of the reaction conditions of oxazinones with carbon nucleophiles led to the synthesis of a series of 4‐hydroxy‐quinolin‐2‐ones and 4‐hydroxy‐1,8‐naphthyridin‐2‐ones in high yields, whereas reaction with a variety of alcohols proceeded smoothly to the formation of the corresponding N‐acetyl‐anthranilates and nicotinates.     

Di‐2‐pyridyl ketone 4‐methyl‐4‐phenyl­thio­semicarbazone

The mol­ecule of the title compound, C₁₉H₁₇N₅S, adopts a Z configuration about the azomethine bond and exists as the thione tautomer. The overall structure of the mol­ecule is distributed in four different planes. An intramolecular hydrogen bond involving the pyridyl N atom and the H atom attached to the hydrazine N atom leads to the formation of a six‐membered ring.     

Synthesis of 1‐methyl‐, 4‐nitro‐, 4‐amino‐and 4‐iodo‐1,2‐dihydro‐3H‐pyrazol‐3‐ones

4‐Aminopyrazole‐3‐ones 4b, e, f were prepared from pyrazole‐3‐ones 1b‐d in a four‐step reaction sequence. Reaction of the latter with methyl p‐toluenesulfonate gave 1‐methylpyrazol‐3‐ones 2b‐d . Compounds 2b‐d were treated with aqueous nitric acid to give 4‐nitropyrazol‐3‐ones 3b‐d. Reduction of compounds 3b‐d by catalytic hydrogenation with Pd‐C afforded the 4‐amino compounds 4b, e, f. Using similar reaction conditions, nitropyrazole‐3‐ones derivatives 2c, d were reduced into aminopyrazole‐3‐ones 5e, f. 4‐Iodopyrazole‐3‐ones 7a, 7c and 8 were prepared from the corresponding pyrazol‐3‐ones 2a, 2c and 6 and iodine monochloride or sodium azide and iodine monochloride.