The Astounding Chemistry of a 2‐Amino‐1,2‐dihydroisoquinoline Derivative

The cycloadducts of isoquinolinium N‐phenyl imide 2 with C=C bonds are derivatives of 2‐amino‐1,2‐dihydroisoquinoline. Their N^β‐vinylphenylhydrazine system is amenable to an acid‐catalyzed [3,3]‐sigmatropic shift; the formation of pentacyclic aminals is exemplified by 6 → 8 . The dimethyl maleate adduct 11 , C₂₁H₂₀N₂O₄, is exceptional by being converted on treatment with acid to bright‐yellow crystals, C₂₄H₂₂N₂O₆ (additional C₃H₂O₂). X‐Ray crystal‐structure analysis and NMR spectra reveal structure 13 , and mechanistic studies indicated an initial β‐elimination at the N−N bond of 11 to yield 18 ; this step is followed by a retro‐Mannich‐type cleavage that gives methyl isoquinoline‐1‐acetate ( 14 ) and methyl 2‐(phenylimino)acetate ( 15 ), according to the sequence C₂₁H₂₀N₂O₄ ( 11 )→ 18 →C₁₂H₁₁NO₂ ( 14 )+C₉H₉NO₂ ( 15 ). In the second act of the drama, electrophilic attack by 15 ‐H⁺ on the ene‐hydrazine group of a second molecule of 11 furnishes 13 by a polystep intramolecular redox reaction. All rate constants must be fine‐tuned in this reaction cascade to give 13 in yields of up to 78% with an overall stoichiometry: 2 C₂₁H₂₀N₂O₄ ( 11 )→C₂₄H₂₂N₂O₆ ( 13 )+C₁₂H₁₁NO₂ ( 14 )+aniline. Interception and model experiments confirmed the above pathway. A by‐product, C₃₃H₃₁N₃O₆ ( 62 ), arises from an acid‐catalyzed dimerization of 11 and subsequent elimination of 15 .     

Four Syntheses of 4‐Amino‐3,5‐dinitropyrazole

In this paper, syntheses of 4‐amino‐3,5‐dinitropyrazole from four different starting materials are described. The starting materials were 4‐nitropyrazole, 4‐nitro‐3,5‐dimethylpyrazole, 3,5‐dinitropyrazole, and 4‐chloropyrazole, respectively. They are compared in terms of yield, number of steps and suitability for scale‐up into pilot scale production. The overall yield, calculated from commercially available starting materials, ranged from 21% in the case of synthesis via 3,5‐dinitropyrazole up to 61% for the one starting from 4‐chloropyrazole. With numerous factors taken into account, the latter was chosen for a pilot scale study and the product could be produced in batches of 200 g.     

Unveiling 79‐Year‐Old Ixene and Its BN‐Doped Derivative

Polycyclic aromatic hydrocarbons (PAHs) are key components of organic electronics. The electronic properties of these carbon‐rich materials can be controlled through doping with heteroatoms such as B and N, however, few convenient syntheses of BN‐doped PAHs have been reported. Described herein is the rationally designed, two‐step syntheses of previously unknown ixene and BN‐doped ixene (B₂N₂‐ixene), and their characterizations. Compared to ixene, B₂N₂‐ixene absorbs longer‐wavelength light and has a smaller electrochemical energy gap. In addition to its single‐crystal structure, scanning tunneling microscopy revealed that B₂N₂‐ixene adopts a nonplanar geometry on a Au(111) surface. The experimentally obtained electronic structure of B₂N₂‐ixene and the effect of BN‐doping were confirmed by DFT calculations. This synthesis enables the efficient and convenient construction of BN‐doped systems with extended π‐conjugation that can be used in versatile organic electronics applications.     

2‐Amino‐7‐chloro‐2′‐deoxy­tubercidin

In 4‐chloro‐7‐(2‐de­oxy‐β‐d ‐erythro‐pento­furanos­yl)‐7H‐pyr­rolo­[2,3‐d]­pyrimidine‐2,4‐diamine, C₁₁H₁₄ClN₅O₃, the conformation of the N‐glycosylic bond is between anti and high‐anti [χ = −102.5 (6)°]. The 2′‐deoxy­ribofuranosyl unit adopts the C3′‐endo‐C4′‐exo (³T₄) sugar pucker (N‐type) with P = 19.6° and τ_m = 32.9° [terminology: Saenger (1989). Landolt‐Börnstein New Series, Vol. 1, Nucleic Acids, Subvol. a, edited by O. Madelung, pp. 1–21. Berlin: Springer‐Verlag]. The orientation of the exocyclic C4′—C5′ bond is +ap (trans) with a torsion angle γ = 171.5 (4)°. The compound forms a three‐dimensional network that is stabilized by four inter­molecular hydrogen bonds (N—H⋯O and O—H⋯N) and one intra­molecular hydrogen bond (N—H⋯Cl).     

5‐Amino‐4‐(4‐diethylaminophenyl)‐2‐phenyl‐7‐(pyrrolidin‐1‐yl)‐1,6‐naph­thyridine‐8‐carbonitrile

In the title compound, C₂₉H₃₀N₆, the naphthyridine ring is almost planar with a dihedral angle of 5.4 (1)° between the pyridyl rings. The dihedral angles between the naphthyridine system and the diethyl­amino­phenyl, phenyl and pyrrolidine rings are 53.1 (1), 19.8 (1) and 20.9 (1)°, respectively. The pyrrolidine ring adopts a half‐chair conformation. The mol­ecule is stabilized by weak C—H?N interactions.     

3‐Amino‐1,2,4‐triazine

In the crystal structure of 3‐amino‐1,2,4‐triazine, C₃H₄N₄, the mol­ecules form hydrogen‐bonded chains that are almost parallel to the b axis (3.2°), and which are inclined to the a and c axes by ～21 and ～69°, respectively. The distortion of the 1,2,4‐triazine ring in the crystal is compared with gas‐phase ab initio molecular‐orbital calculations.     

Capture of 3‐Amino‐4‐oxycyanofurazan and Characterization of Isoxazole Product

1,3‐Dipolar cycloaddition reaction between nitrile oxide and alkyne was used to capture 3‐amino‐4‐oxycyanofurazan (AOCF), which was considered as the key intermediate during the synthesis of 3,4‐bis(4‐aminofurazano‐3‐yl)furoxan (DATF) from 3‐amino‐4‐chloroximinofurazan. The isolated isoxazoles from the reaction afforded evidences for the existence of AOCF. The structures of the isoxazoles were characterized by IR, ¹H NMR, ¹³C NMR, MS, and elemental analysis. In addition, single crystal X‐ray diffraction of one isoxazole was obtained.     

4‐Amino‐N‐isopropyl­benzamidinium chloride ethanol solvate

The title compound, C₁₀H₁₆N·Cl⁻·C₂H₆O, is an important intermediate in the convergent synthesis of amidine‐substituted polycyclic heterocycles, a class of compounds that shows significant anticancer activity. The molecule of (I) is not planar, having a dihedral angle of 25.00 (7)° between the aniline and amidine (–C—NH=C=NH₂) groups. The proton­ation of the amidine molecular fragment is accompanied by delocalized C—N bond distances of 1.320 (2) and 1.317 (2) Å. The cations and chloride anions are involved in a network of hydrogen bonds, resulting in the formation of infinite chains propagating along the b direction. The chains are further grouped within the ab plane, in such a way that the structure is segregated into layers dominated by hydro­phobic interactions involving N‐isopropyl residues and layers dominated by N—H⋯Cl [N⋯Cl = 3.275 (2)–3.596 (2) Å], O—H⋯Cl [O⋯Cl = 3.229 (3) Å] and N—H⋯O [N⋯O = 2.965 (3) Å] hydrogen bonds.     

5‐Amino‐4‐(4‐diethyl­amino­phenyl)‐2‐(4‐hydroxy­phenyl)‐7‐(pyrrolidin‐1‐yl)‐1,6‐naphthyridine‐8‐carbo­nitrile

In the title compound, C₂₉H₃₀N₆O, the naphthyridine moiety is planar with a dihedral angle between the fused rings of 1.9 (1)°. The phenol ring is nearly coplanar, while the diethyl­amino­phenyl substituent is orthogonal to the central naphthyridine ring and the pyrrolidine ring makes an angle of 11.2 (1)° with it. The O atom of the hydroxy substituent is coplanar with the phenyl ring to which it is attached. The molecular structure is stabilized by a C—H?N‐type intramolecular hydrogen bond and the packing is stabilized by intermolecular C—H?π, O—H?N and N—H?O hydrogen bonds.     

2‐Amino‐4‐(4‐pyridyl)­pyrimidine and the 1:1 adduct with 4‐amino­benzoic acid

The structure of the title compound, C₉H₈N₄, comprises non‐planar mol­ecules that associate via pyrimidine N—H?N dimer R(8) hydrogen‐bonding associations [N?N 3.1870 (17) Å] and form linear hydrogen‐bonded chains via a pyrimidine N—H?N(pyridyl) interaction [N?N 3.0295 (19) Å]. The dihedral angle between the two rings is 24.57 (5)°. The structure of the 1:1 adduct with 4‐amino­benzoic acid, C₉H₈N₄·C₇H₇NO₂, exhibits a hydrogen‐bond­ing network involving COOH?N(pyridyl) [O?N 2.6406 (17) Å], pyrimidine N—H?N [N?N 3.0737 (19) and 3.1755 (18) Å] and acid N—H?O interactions [N?O 3.0609 (17) and 2.981 (2) Å]. The dihedral angle between the two linked rings of the base is 38.49 (6)° and the carboxyl­ic acid group binds to the stronger base group in contrast to the (less basic) complementary hydrogen‐bonding site.     

A Terminal,Fluxional η4‐Benzene Complex with a Thermally Accessible Triplet State is the Primary Photoproduct in the Intercyclobutadiene Haptotropism of (CpCo)phenylenes

Low‐temperature irradiation of linear [3]‐ and [4]phenylene cyclopentadienylcobalt complexes generates labile, fluxional η⁴‐arene complexes, in which the metal resides on the terminal ring. Warming induces a haptotropic shift to the neighboring cyclobutadiene rings, followed by the previously reported intercyclobutadiene migration. NMR scrutiny of the primary photoproduct reveals a thermally accessible 16‐electron cobalt η²‐triplet species, which, according to DFT computations, is responsible for the rapid symmetrization of the molecules along their long axes. Calculations indicate that the entire haptotropic manifold along the phenylene frame is governed by dual‐state reactivity of alternating 18‐electron singlets and 16‐electron triplets.     

Reaction of Amidrazones with Diaminomaleonitrile: Synthesis of 4‐Amino‐5‐Iminopyrazoles

Diaminomaleonitrile and N‐arylbenzamidrazones reacted together to give 4‐amino‐5‐iminopyrazoles. A probable reaction mechanism involves firstly removal of ammonia, followed by addition and cylization of the hydrazino‐N ² of amidrazone to the nitrile group in diaminomaleonitrile. The structure of the obtained products was proved by IR, mass, NMR spectra and elemental analyses.     

Coordination Compounds of Palladium(II) and 4‐Amino‐1,2,4‐triazole

Mononuclear coordination compounds of the type [Pd(NH₂trz)₄]²⁺ with the counterions chloride, nitrate, trifluoromethanesulfonate, and methanesulfonate were synthesized and their structures identified with single‐crystal X‐ray diffraction. In case of the synthesis with methanesulfonate as the counterion the dominant product was of the generic formula [Pd₂(NH₂trz)₃](CH₃SO₃)₄, and the complex [Pd(NH₂trz)₄](CH₃SO₃)₂ only emerged as a byproduct. While the structure of the byproduct could be analyzed by single‐crystal X‐ray diffraction, suitable crystals of the main product [Pd₂(NH₂trz)₃](CH₃SO₃)₄ could not be obtained. However, stoichiometry implies a polynuclear nature with NH₂trz present in the rare μ₃‐η¹:η¹:η¹ coordination type, i.e. with NH₂trz molecules coordinating to three palladium atoms. Accordingly, identification of solids by single‐crystal analysis alone can be misleading in particular with NH₂trz as a ligand due to its versatile coordination behavior. Finally, analysis by differential scanning calorimetry (DSC) revealed that the complexes were thermally stable (the onset of decomposition well above 100 °C), with [Pd₂(NH₂trz)₃](CH₃SO₃)₄ being the most stable compound (onset of decomposition at 204 °C).     

Organocatalyzed Enantioselective Synthesis of 2‐Amino‐4H‐chromene Derivatives

Optically active 2‐amino‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carboxylates, 2‐amino‐5‐oxo‐5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitriles, and 2‐amino‐8‐oxo‐5,6,7,8‐tetrahydro‐4H‐chromene‐3‐carbonitriles were synthesized. Using cinchona alkaloid‐derived bifunctional catalysts, the corresponding 2‐amino‐4H‐chromene derivatives were obtained in high yields and moderate to high ee values (up to 82% ee) from the tandem Michael addition–cyclization reaction between 1,3‐cyclohexanediones or 1,2‐cyclohexanediones and (E )‐3‐aryl‐2‐cyanoacrylate or alkylidene malononitrile derivatives.     

4‐Amino‐TEMPO as N‐Nucleophile in Palladium‐Catalyzed Aminocarbonylation

Palladium‐catalyzed aminocarbonylation of iodobenzene and iodoalkenes (1‐iodocyclohexene, 4‐tert‐butyl‐1‐iodocyclohexene, α‐iodostyrene, 17‐iodoandrost‐16‐ene) was carried out using a free radical (4‐amino‐TEMPO) for the first time. Its reduced form (4‐amino‐2,2,6,6‐tetramethylpiperidine) was also used as N‐nucleophile. The free radical was partially reduced under aminocarbonylation conditions; however, the isolation of carbonylated products bearing a stable radical moiety was successfully accomplished. It was proved that the reduction of the 1‐oxyl functionality took place to higher extent when more severe conditions (40 bar CO pressure) were used. The mixture of carboxamide and 2‐ketocarboxamide products was obtained using iodobenzene because of single and double carbon monoxide insertion, respectively. In turn, carboxamide derivatives were formed exclusively when iodoalkenes were used as substrates.     

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.