Synthesis and Chemical Reactivity of Pyrano[3,2‐c]quinolinones

The present review covers the methods developed for the synthesis of different pyrano[3,2‐c]quinolinones as well as the chemical reactivity of these compounds towards various types of chemical reactions.     

Synthesis of New 2‐Phenylpyrano[3,2‐b]phenothiazin‐4(6H)‐one Derivatives

A new synthesis of 2‐phenylpyrano[3,2‐b]phenothiazin‐4(6H)‐one derivatives was reported. First 2,10‐diacetyl‐3‐hydroxyphenothiazine ( 2 ) was converted into their benzoyloxy esters ( 3a – 3j ) using different aromatic carboxylic acids in the presence of phosphorous oxychloride in pyridine. Benzoyloxy esters were converted into their 1,3‐diones ( 4a – 4j ) by using dry KOH in pyridine via Baker‐Venkataraman transformation reaction. The 1,3‐diones thus obtained were cyclised to pyranophenothiazines ( 5a – 5j ) by refluxing in an acetic acid/HCl mixture.     

Fine Control of the Redox Reactivity of a Nonheme Iron(III)–Peroxo Complex by Binding Redox‐Inactive Metal Ions

Redox‐inactive metal ions are one of the most important co‐factors involved in dioxygen activation and formation reactions by metalloenzymes. In this study, we have shown that the logarithm of the rate constants of electron‐transfer and C−H bond activation reactions by nonheme iron(III)–peroxo complexes binding redox‐inactive metal ions, [(TMC)Fe^III(O₂)]⁺‐M^{n +} (M^{n +}=Sc³⁺, Y³⁺, Lu³⁺, and La³⁺), increases linearly with the increase of the Lewis acidity of the redox‐inactive metal ions (ΔE ), which is determined from the g_zz values of EPR spectra of O₂^.−‐M^{n +} complexes. In contrast, the logarithm of the rate constants of the [(TMC)Fe^III(O₂)]⁺‐M^{n +} complexes in nucleophilic reactions with aldehydes decreases linearly as the ΔE value increases. Thus, the Lewis acidity of the redox‐inactive metal ions bound to the mononuclear nonheme iron(III)–peroxo complex modulates the reactivity of the [(TMC)Fe^III(O₂)]⁺‐M^{n +} complexes in electron‐transfer, electrophilic, and nucleophilic reactions.     

Synthesis and Reactivity in [3+2] Cycloadditions of Isoxanthopterin N(5)‐Oxides – A New Synthesis of 6‐Substituted Pteridinediones

Intramolecular condensation of the N‐(4‐amino‐5‐nitrosopyrimidin‐4‐yl)‐2‐chloroacetamide 2 led to the pteridinone N(5)‐oxide 4 , while treatment of 2 with Me₃P yielded the 8‐(chloromethyl)purine 3 . A high‐yielding [3+2] dipolar cycloaddition of the N(5)‐oxide 4 to electron‐poor dipolarophiles, followed by spontaneous N,O‐bond cleavage, gave the C(6)‐substituted pteridinones 8a – 8d that were deprotected to provide the pteridine‐4,7(3H,8H)‐diones 9a – 9d , constituting a new synthesis of pterinones possessing a functionalised side chain at C(6).     

Spectroscopic Capture and Reactivity of a Low‐Spin Cobalt(IV)‐Oxo Complex Stabilized by Binding Redox‐Inactive Metal Ions

High‐valent cobalt‐oxo intermediates are proposed as reactive intermediates in a number of cobalt‐complex‐mediated oxidation reactions. Herein we report the spectroscopic capture of low‐spin (S=1/2) Co^IV‐oxo species in the presence of redox‐inactive metal ions, such as Sc³⁺, Ce³⁺, Y³⁺, and Zn²⁺, and the investigation of their reactivity in C? H bond activation and sulfoxidation reactions. Theoretical calculations predict that the binding of Lewis acidic metal ions to the cobalt‐oxo core increases the electrophilicity of the oxygen atom, resulting in the redox tautomerism of a highly unstable [(TAML)Co^III(O^.)]^2? species to a more stable [(TAML)Co^IV(O)(Mⁿ⁺)] core. The present report supports the proposed role of the redox‐inactive metal ions in facilitating the formation of high‐valent metal–oxo cores as a necessary step for oxygen evolution in chemistry and biology.     

Chemical Reactivity of 4,9‐Dimethoxy‐5‐oxo‐5H‐furo[3,2‐g]chromene‐6‐Carboxaldehyde Toward Some Nucleophilic Reagents

The chemical reactivity of 4,9‐dimethoxy‐5‐oxo‐5H‐furo[3,2‐g ]chromene‐6‐carboxaldehyde (6‐formylkhellin) ( 1 ) was studied toward a diversity of nitrogen nucleophilic reagents. Reaction of carboxaldehyde 1 with some primary amines and heterocyclic amines afforded the corresponding Schiff bases. Also, the reactivity of carboxaldehyde 1 was studied toward some hydrazine derivatives, namely 7‐chloro‐4‐hydrazinoquinoline, 3‐hydrazino‐5,6‐diphenyl‐1,2,4‐triazine, N⁴‐phenylthiosemicarbazide, and S‐benzyldithiocarbazate. 6‐Formylkhellin ( 1 ) underwent ring transformation upon treatment with hydroxylamine hydrochloride producing 5‐hydroxy‐4,9‐dimethoxy‐7‐oxo‐7H‐furo[3,2‐g ]chromene‐6‐carbonitrile ( 22 ). Some pyrimidine, [1,2,4]triazolo[4,3‐a ]pyrimidine, tetrazolo[1,5‐a ]pyrimidine, and diazepine derivatives linked benzofuran were efficiently synthesized. Reaction of carboxaldehyde 1 with a variety of 1,4‐binucleophiles produced furochromone‐fused benzodiazepine, pyridotriazepine, benzoxazepine, and benzothiazepine derivatives. Some unsymmetrical thiocarbohydrazones were also synthesized. Structures of the new synthesized products were deduced on the basis of their analytical and spectral data.     

trans‐Cyano(6‐methyl‐1,4,8,11‐tetraazacyclotetradecan‐6‐amine)cobalt(III) bis(perchlorate) hydrate and trans‐hydroxo(6‐methyl‐1,4,8,11‐tetraazacyclotetradecan‐6‐amine)cobalt(III) bis(perchlorate)

The crystal structures of a pair of closely related macrocyclic cyano‐ and hydroxopenta­amine­cobalt(III) complexes, as their perchlorate salts, are reported. Although the two complexes, [Co(CN)(C₁₁H₂₇N₅)](ClO₄)₂·H₂O and [Co(OH)(C₁₁H₂₇N₅)](ClO₄)₂, exhibit similar conformations, significant differences in the Co—N bond lengths arise from the influence of the sixth ligand (cyano as opposed to hydroxo). The ensuing hydrogen‐bonding patterns are also distinctly different. Disorder in the perchlorate anions was clearly resolved and this was rationalized on the basis of distinct hydrogen‐bonding motifs involving the anion O atoms and the N—H and O—H donors.     

Synthesis of Some Novel Heteroannulated Pyrano[3,2‐c]quinoline‐2,5(6H)‐diones

6‐Butyl‐3‐((dimethylamino)methylene)pyrano[3,2‐c]quinolinone and 6‐butyl pyrano[3,2‐c]quinolone‐3‐carbonitrile were efficiently synthesized in good yield. These two new precursors were used to obtain some novel heteroannulated pyrano[3,2‐c]quinolone derivatives from heterocyclization reactions with various binucleophiles. These heteroannulation reactions afforded novel heterocyclic systems fused to the pyranoquinolinone at face c, such as pyrazole, pyrimidine, pyridine, and pyrazolopyranone.     

Mono‐ and Perfluoroaryliodine(III) Cyano Compounds – Synthesis,Reactivity, and Structure

C₆F₅I(CN)₂ and x‐FC₆H₄I(CN)₂ (x = 2, 3, 4) were isolated from reactions of the corresponding aryliodine difluorides ArIF₂ and a stoichiometric excess of Me₃SiCN in CCl₃F (0 °C) or CH₂Cl₂ (20 °C), respectively. In addition, x‐FC₆H₄I(CN)₂ compounds were synthesized in good yields on alternative routes, namely from 3‐ or 4‐FC₆H₄I(OC(O)CH₃)₂ or 4‐FC₆H₄I(OC(O)CF₃)₂ or from 4‐FC₆H₄IO and Me₃SiCN in CH₂Cl₂ at 20 °C. In the 1 : 1 reaction of C₆F₅IF₂ and Me₃SiCN a lower temperature was necessary to suppress partial disubstitution and to obtain the first example of a new type of aryliodine(III) cyanide compounds, C₆F₅I(CN)F. 4‐FC₆H₄I(CN)F could be isolated from the equimolar reaction of 4‐FC₆H₄IF₂ and Me₃SiCN in CH₂Cl₂ even at 20 °C. The new products were characterized by multi‐NMR and Raman spectroscopy. The molecular structures of C₆F₅I(CN)₂, 3‐ and 4‐FC₆H₄I(CN)₂, C₆F₅I(CN)F, and 4‐FC₆H₄I(CN)F are discussed and compared with that of C₆F₅IF₂. The reactivity of C₆F₅I(CN)F towards fluoride acceptors EF_n (BF₃, AsF₅) and R_xEX_?x (C₆F₅SiF₃, C₆H₅SiF₃, C₆H₅PF₄, Me₃SiCl, Me₃SiC₆F₅) were investigated and showed differing reaction patterns (fluoride abstraction, aryl transfer, chloride transfer). Besides the molecular entities C₆F₅I(CN)F and C₆F₅I(CN)Cl, the corresponding iodonium salts [C₆F₅(CN)I][BF₄] and [C₆F₅(CN)I][AsF₆] were isolated. The thermal stability of ArI(CN)₂ and ArI(CN)F, neat and in solution, as well as the reactivity of 4‐FC₆H₄I(CN)₂ towards the Lewis acid BF₃ are reported.     

Metal Derivatives of 1,3‐Imidazolidine‐2‐thione with Divalent d10 Metal Ions (Zn–Hg) : Synthesis and Structures

Reactions of divalent Zn‐Hg metal ions with 1,3‐imidazolidine‐2‐thione (imdtH₂) in 1 : 2 molar ratio have formed monomeric complexes, [Zn(η¹‐S‐imdtH₂)₂(OAc)₂] ( 1 ), [Cd((η¹‐SimdtH₂)₂I₂] ( 2 ), [Cd(η¹‐S‐imdtH₂)₂Br₂] ( 3 ), and [Hg(η¹‐S‐imdtH₂)₂I₂] ( 4 ). Complexes 1 – 4 , have been characterized by elemental analysis (C, H, N), spectroscopy (IR, ¹H, NMR) and x‐ray crystallography ( 1 ‐ 4 ). Hydrogen bonding between oxygen of acetate and imino hydrogen of ligand, {N(2)–H(2C)···O(2)^#} in 1 , ring CH and imino hydrogen, {C(2A)–H(2A)···Br(2)^#} in 3 have formed H‐bonded dimers. Similarly, the interactions between molecular units of complexes 2 and 4 have yielded 2D polymers. The polymerization occurs via intermolecular interactions between thione sulfur and imino hydrogen, {N(2)–H(2)···S(1)^#}, imino hydrogen and the iodine atom, {NH(1)···I(2)^#} in 2 and imino hydrogen – iodine atom {N(2A)–H(2A)···I(2)} and I···I interaction in 4 . Crystal data: [Zn(η¹‐S‐imdtH₂)₂(OAc)₂] ( 1 ), C₁₀H₁₈N₄O₄S₂Zn, orthorhombic, Pbcn, a = 9.3854(7) Å, b = 12.4647(10) Å, c = 13.2263(11) Å; V = 1547.3(2) ų, Z = 4, R = 0.0280 [Cd((η¹‐S‐imdtH₂)₂I₂] ( 2 ), C₆H₁₂CdI₂N₄S₂, orthorhombic, Pnma, a = 13.8487(10) Å, b = 14.4232(11) Å, c = 7.0659(5) Å; Z = 4, V = 1411.36(18) ų, R = 0.0186.     

N‐Methylimidazolkomplexe des Berylliums: [Be(Me‐Im)4]I2 und [Be3(μ‐OH)3(Me‐Im)6]Cl3

Tetra(N‐methylimidazole)‐beryllium‐di‐iodide, [Be(Me‐Im)₄]I₂ ( 1 ), was prepared from beryllium powder and iodine in N‐methylimidazole suspension to give yellow single crystal plates, which were characterized by X‐ray diffraction and IR spectroscopy. Compound 1 crystallizes tetragonally in the space group I 2d with four formula units per unit cell. Lattice dimensions at 100(2) K: a = b = 1784.9(1), c = 696.2(1) pm, R₁ = 0.0238. The structure consists of homoleptic dications [Be(Me‐Im)₄]²⁺ with short Be–N distances of 170.3(3) pm and iodide ions with weak interionic C–H ··· I contacts. Experiments to yield crystalline products from reactions of N‐methylimidazole with BeCl₂ and (Ph₄P)₂[Be₂Cl₆], respectively, in dichloromethane solutions were unsuccessful. However, single crystals of [Be₃(μ‐OH)₃(Me‐Im)₆]Cl₃ ( 2 ) were obtained from these solutions in the presence of moisture air. According to X‐ray diffraction studies, two different crystal individuals ( 2a and 2b ) result, depending on the starting materials BeCl₂ and (Ph₄P)₂[Be₂Cl₆], respectively [ 2a : Space group P2₁/n, Z = 4; 2b : Space group P , Z = 2]. As a side‐product from the reaction of N‐methylimidazole with (Ph₄P)₂[Be₂Cl₆] single crystals of (Ph₄P)Cl·CH₂Cl₂ ( 3 ) were identified crystallographically (P2₁/n, Z = 4) which are isotypical with the corresponding known bromide (Ph₄P)Br·CH₂Cl₂.     

Synthesis and conversion of 6‐fluoro derivatives of 1,3,4‐thiadiazolo‐[3,2‐a]pyrimidine

2‐Alkyl‐, 2‐aryl‐, and 2‐halo‐substituted derivatives of 7‐methyl‐6‐fluoro‐1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐6‐one ( 3 ) were prepared by reaction of 2‐substituted 5‐amino‐1,3,4‐thiadiazoles ( 1 ) and ethyl 2‐fluoroacetoacetate ( 2 ) in polyphosphoric acid. A convenient procedure was developed for the synthesis of new 2‐amino derivatives of 2‐R‐7‐methyl‐6‐fluoro‐1,3,4‐thiadiazolo[3,2‐a]pyrimidin‐6‐one ( 5 ). J. Heterocyclic Chem., (2011).     

New Method for the Synthesis and Reactivity of (5‐R‐1,3,4‐Oxadiazol‐2‐yl)furoxans

A new, simple and general one‐pot method for the preparation of (5‐R‐1,3,4‐oxadiazol‐2‐yl)furoxans has been developed on the basis of the interaction between accessible 3‐methylfuroxan‐4‐carboxylic acid hydrazide and aliphatic, aromatic and heterocyclic carboxylic acids or their chlorides in the presence of POCl₃. The synthesis and study of (5‐R‐1,3,4‐oxadiazol‐2‐yl)furoxans reactivity resulted in new polyheterocyclic ensembles incorporating furoxan, 1,3,4‐oxadiazole, pyrrole, triazole, furan, thiophene, pyrimidine, and other heterocycles in different combinations.     

乙烯基锡修饰的双吡唑甲烷第六族金属羰基化合物的合成与反应

通过双吡唑基甲基锂与二苯基乙烯基碘化锡的反应, 合成了桥头碳上带有乙烯基锡修饰的双吡唑甲烷配体。在回流的THF中这些乙烯基锡修饰的双吡唑甲烷配体(R3SnCHPz2, R3Sn为三乙烯基锡或二苯基乙烯基锡;Pz代表取代吡唑)与M(CO)5THF (M = Mo或W)反应产生杂双金属化合物R3SnCHPz2M(CO)3。在这些化合物中,一个乙烯基以h2方式配位到金属钼或钨上,双吡唑甲烷表现为一个三齿k3-(p,N,N)配体。(CH2=CH)3SnCH(3,5-Me2Pz)2W(CO)3和Ph2(CH2=CH)SnCH(3,5-Me2Pz)2W(CO)3与I2的反应也被研究。前者给出化合物CH2(3,5-Me2Pz)2W(CO)4,而后者随着有机锡的丢失产生四元金属杂环化合物CH(3,5-Me2Pz)2W(CO)3I。用PhSNa处理该四元金属杂环化合物导致碘负离子被取代,得到化合物CH(3,5-Me2Pz)2W(CO)3SPh。     

A New Fluorescent Chemosensor for Metal Ions Based upon 1,8‐Naphthalimide and 8‐Hydroxyquinoline

A new fluorescent chemosensor based upon 1,8‐naphthalimide and 8‐hydroxyquinoline was synthesized, and its fluorescent properties in the presence of different metal cations (Hg²⁺, Ag⁺, Zn²⁺, Fe²⁺, Cd²⁺, Pb²⁺, Ca²⁺, Cu²⁺, Mg²⁺, and Ba²⁺) were investigated. It displayed fluorescence quenching with some heavy and transition metal (HTM) ions, and the quenching strongly depended on the nature of HTM ions.