Rearrangement of allylic azide and phenylthio groups of 3′-azido- or 3′-phenylthio-4′,5′-didehydro-5′-deoxyarabinofuranosyluridines

The reversible intramolecular [3,3]-sigmatropic rearrangement between 1-(3-azido-3,5-dideoxy-β-d-threo-pent-4-enofuranosyl)uracil (3) and 1-(5-azido-3,5-dideoxy-β-d-glycero-pent-4-enofuranosyl)uracil (4) and irreversible radical rearrangement of 1-(3,5-dideoxy-3-phenylthio-β-d-threo-pent-4-enofuranosyl)uracil (5) and 1-[3,5-dideoxy-3-(4-tolyl)thio-β-d-threo-pent-4-enofuranosyl]uracil (7) into 1-(3,5-dideoxy-5-phenylthio-β-l-glycero-pent-4-enofuranosyl)uracil (6) and 1-[3,5-dideoxy-5-(4-tolyl)thio-β-l-glycero-pent-3-enofuranosyl]uracil (8) were attained at room temperature.     

Solvent-free reactions of N,N′-thiocarbonyldiimidazole with ferrocenylcarbinols

The efficient and simple routes for the synthesis of various ferrocenyl derivatives from ferrocenylcarbinols and N,N′-thiocarbonyldiimidazole (TCDI) are described. It involves grinding the two substrates in a Pyrex tube with a glass rod at room temperature. The reaction of ferrocenylmethanol (1a) provided S,S-bis(ferrocenylmethyl)dithiocarbonate (1b), whose crystal structure and a plausible mechanism for its formation are also reported. The reaction of 1-ferrocenyl-1-phenylmethanol (2a) and 1-ferrocenylbutanol (2b) gave the products 2c and 2d, respectively. The reaction of ω-ferrocenyl alcohols 4-ferrocenylphenol (3a) and 6-ferrocenylhexan-1-ol (3b) yielded the products 3c and 3d, respectively. Reaction of 1,1′-ferrocenedimethanol (3e) afforded 3f in moderate yield, and by contrast, it was not similar to 1b. Reaction of [4-(trifluoromethyl)phenyl]methanol (4a) provided the thiocarbonate 4b in good yield.     

Structural diversity in the self-assembly of Ag(I) complexes containing 2-amino-5-halopyrimidine

A series of Ag(I) complexes containing the 2-amino-5-halopyrimidine ligands have been synthesized and their structures characterized by X-ray crystallography. The isomorphous complexes Ag(L-Cl)₂(CF₃SO₃) (L-Cl = 2-amino-5-chloropyrimidine), 1, and Ag(L-Br)₂(CF₃SO₃) (L-Br = 2-amino-5-bromopyrimidine), 2, are mononuclear, while [Ag(L-Br)(CF₃SO₃)]₆·6C₄H₁₀O, 3, and [Ag(L-I)(CF₃SO₃)]₆ (L-I = 2-amino-5-iodopyrimidine), 4, show cyclic self-assembly of six Ag(Ι) atoms and six L-X ligands, resulting in 24-membered metallocycles. The complex [Ag(L-I)(CF₃SO₃)]_∞, 5, forms 1D zigzag chains which are linked through C-I?Ag and Ag?O interactions to form a 3D structure. The tetranuclear complexes [Ag(L-X)(NO₃)]₄ [X = Cl, 6; Br, 7] form 16-membered metallocycles, while [Ag(L-X)(ClO₄)]_∞ [X = Cl, 8; Br, 9] exhibit helical chains. The different structure of 5 from 1 and 2 appears to be due to the stronger nucleophilic character of the iodine atom. In these complexes, the relatively smaller NO₃⁻ anions lead to the formation of tetranuclear metallocycles and the larger CF₃SO₃⁻ anions support the hexanuclear metallocycles, whereas the ClO₄⁻ anions induce the helical chains.     

An unexpected formation of pyrazolopyrimidines during the attempted to obtain 5-substituted tetrazoles from carbonitriles

In this Letter, we described the synthesis of new 5-(5-amino-1-aryl-1H-pyrazole-4-yl)-1H-tetrazoles 2a–c from 5-amino-1-aryl-1H-pyrazole-4-carbonitriles 1a–c as well as the unexpected 1H-pyrazolo[3,4-d]pyrimidine derivatives 6a–c from 5-amino-1-aryl-3-methyl-1H-pyrazole-4-carbonitriles 4a–c, instead of 5-(5-amino-1-aryl-3-methyl-1H-pyrazole-4-yl)-1H-tetrazoles 5a–c as desired. In an attempt to obtain these tetrazole derivatives containing the methyl group at C3-position in the pyrazole ring, the amino group in 5-amino-1-(4-methoxyphenyl)-3-methyl-1H-pyrazole-4-carbonitrile 4c was protected by the reaction with sodium hydride and di-tert-butyl-dicarbonate (Boc). The tetrazole derivative 5c was synthesized from the protected compound 7c using analogue methodology to obtain 2a–c and 6a–c.     

Stabilization of (N-methyleneamino)imidoylketenes: synthesis of dipyrazolo[1,2-a;1′,2′-d][1,2,4,5]tetrazines

Thermolysis of substituted methyl 1-methyleneamino-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates 2a,b led to substituted dimethyl 3,9-dioxo-1,5,7,11-tetrahydro-1H,7H-dipyrazolo[1,2-a;1′,2′-d][1,2,4,5]tetrazine-1,7-dicarboxylates 4a,b and methyl 2,5-dihydro-5-oxo-1H-pyrazole-3-carboxylates 5a,b as minor products. The structure of compound 4a was determined by X-ray crystallography. The proposed mechanism of this conversion includes generation of (N-methyleneamino)imidoylketenes 6a,b and its intramolecular transformation to azomethine imines—5-oxo-2,5-dihydropyrazole-1-methylium-2-ides 7a,b, which undergo dimerization in head-to-tail manner yielding products 4a,b and partially hydrolyse to compounds 5a,b.     

Highly selective synthesis of 4(5)-aryl-, 2,4(5)-diaryl-, and 4,5-diaryl-1H-imidazoles via Pd-catalyzed direct C-5 arylation of 1-benzyl-1H-imidazole

Highly selective, practical, and efficient protocols for the preparation of 4(5)-aryl-1H-imidazoles 2, 2,4(5)-diaryl-1H-imidazoles 3, and 4,5-diaryl-1H-imidazoles 1 are described. A key step of these protocols is the regioselective synthesis of 5-aryl-1-benzyl-1H-imidazoles 9 by Pd-catalyzed direct C-5 arylation of commercially available 1-benzyl-1H-imidazole (8) with aryl halides. The three-step synthesis of compounds 3 from 8 also involves the Pd-catalyzed and Cu-mediated direct C-2 arylation of imidazoles 9 with aryl halides under base-free and ligandless conditions. On the other hand, the four-step synthesis of imidazoles 1 from 8 also involves the regioselective bromination of compounds 9 and a Suzuki reaction of the resulting 5-aryl-1-benzyl-4-bromo-1H-imidazoles 11 with arylboronic acids 5 under phase-transfer conditions, followed by N-debenzylation.     

Synthesis, crystal structures, and photochromic properties of 6,6′ or 7,7′ or 6,7′-dimethyl-[2,2′-bi-1H-indene]-3,3′-diethyl-3,3′-dihydroxy-1,1′-diones

New photochromic title compounds 1, 2, and 3 have been prepared starting from 4-methylphthalic anhydride. Compounds 3a and 3b are a pair of enantiomers and were obtained as a racemic mixture (numbered as 3). Compounds 1, 2, and 3 were successfully separated from the isomeric mixture product through fractional crystallization, and their structures are confirmed by X-ray crystallographic analysis. UV-vis absorption and photochromic properties of 1, 2, and 3 have also been investigated. Results reveal that the substituents, even like the simple methyl, on the benzene rings of biindenylidenedione could considerably affect the photochromic property, as well as other properties of this kind of compounds.     

Synthesis of (E)-diethyl 6,6′-(diazene-1,2-diyl)bis(5-cyano-2-methyl-4-phenylnicotinates), a new type of 2,2′-azopyridine dyes

An unexpected, but simple method for the efficient synthesis of new 2.2′-azopyridine dyes, such as (E)-diethyl 6,6′-(diazene-1,2-diyl)bis(5-cyano-2-methyl-4-phenylnicotinates) (2, 4, 6, 8, 10, and 12), based on the treatment of ethyl 6-amino-5-cyano-2-methyl-4-arylnicotinates (1, 3, 5, 7, 9, and 11) with NBS/benzoyl peroxide, is described. The X-ray diffraction analysis and the UV-vis absorption spectra of dye 2 are reported and discussed.     

Substituted coumarin amidines: useful building blocks for the preparation of [1]benzopyrano[4,3-b]pyridin-5-one and [1]benzopyrano[4,3-d]pyrimidin-5-one derivatives

The synthesis of [1]benzopyrano[4,3-b]pyridin-5-ones 4a-f and 4g-j starting from 3-formylcoumarin and 3-cyanocoumarin N-functionalized amidines 3a-f and 3g-j, respectively, was reported. The ring-closure reaction mechanism, under basic or acidic media, was proposed. Furthermore, the reaction of 3-formylamidines 3a,c-f with ammonium acetate gave good yields of 2-substituted [1]benzopyrano[4,3-d]pyrimidin-5-ones 7.     

A simple synthesis of 4-(2-aminoethyl)-5-hydroxy-1H-pyrazoles

A simple four-step synthesis of 4-(2-aminoethyl)-5-hydroxy-1H-pyrazoles 8 (or their 1H-pyrazol-3(2H)-one tautomers 8′) as the pyrazole analogues of histamine was developed. First, enamino lactam 3 was prepared as the key intermediate in two steps from 2-pyrrolidinone (1). Next, acid-catalysed ‘ring switching’ transformations of 3 with monosubstituted hydrazines 4 gave N-[(1-substituted 5-hydroxy-1H-pyrazol-4-yl)ethyl]benzamides 7a-k and N-[2-(2-heteroaryl-3-oxo-2,3-dihydro-1H-pyrazol-4-yl)ethyl]benzamides 7′l-o. Benzamides 7a-k and 7′l-o were finally hydrolysed by heating in 6 M hydrochloric acid to furnish 1-substituted 4-(2-aminoethyl)-5-hydroxy-1H-pyrazoles 8a-k and 4-(2-aminoethyl)-2-heteroaryl-1H-pyrazol-3(2H)-ones 8′l-o in good overall yields.     

Syntheses, spectroscopic and structural characterizations and metal ion binding properties of Schiff bases derived from 4′-aminobenzo-15-crown-5

A series of benzyloxybenzaldehyde derivatives (1-4) were synthesized by the reactions of 4-(bromomethyl)benzonitrile with 4-hydroxy-3-methoxybenzaldehyde (vanillin), 2-hydroxy-3-methoxybenzaldehyde (o-vanillin), 2-hydroxy-4-methoxybenzaldehyde and 2-hydroxy-5-methoxybenzaldehyde. Condensation reactions among the new benzyloxybenzaldehyde derivatives (1-4) with 4′-aminobenzo-15-crown-5 yielded the new Schiff base compounds (5-8). Sodium complexes (5a-8a) and potassium complexes (5b-8b) were prepared with NaClO₄ and KI, respectively. All of these synthesized compounds were characterized on the basis of FT-IR, ¹H and ¹³C NMR, mass spectrometry and elemental analyses data. The solid state structures of compounds 8 and 5a were determined by X-ray crystallography. The extraction abilities of compounds 5-8 were also evaluated in CH₂Cl₂ by using several main group and transition metal picrates, such as Na⁺, K⁺, Pb²⁺, Cr³⁺, Ni²⁺, Cu²⁺ and Zn²⁺.     

Synthesis and properties of novel crown ether-annelated 4′,5′-diaza-9′-(1,3-dithiole-2-ylidene)-fluorenes and their ruthenium(II) complexes

Two novel redox-active 1,3-dithiole (DT) ring-fused 4,5-diazafluorene ligands with crown ether moieties (L1 and L2) were synthesized and characterized. The crystal structure of L1 was studied. The electrochemical and spectroscopic properties of these new ligands, as well as the corresponding bis(bipyridine)ruthenium(II) complexes [4: Ru L1(bpy)₂ and 5: Ru L2(bpy)₂], were also been investigated.     

EPR studies on H-abstraction from methylbenzenes by “magic blue” reagent

After mixing a methylbenzene 4 with “magic blue” solution in F113 (CClF₂CCl₂F) containing bis{perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl}nitroxide 2 and perfluoro-1-nitroso-1-[1-(2-fluorosulfonyl)ethoxy]ethane 3 at room temperature, benzylic H-atom of 4 could be selectively abstracted by 2, and benzyl radical 5 thus generated was immediately trapped by 3. Based on hyper-fine splitting constants (hfsc), the structure of the spin adducts perfluoro[1-(2-fluorosulfonyl)ethoxy]ethyl benzyl nitroxides 6 derived from seven methylbenzenes have been identified. The mechanism of the H-abstraction/spin trapping process is also discussed.     

Regioselective synthesis of 4- and 5-oxazole-phosphine oxides and -phosphonates from 2H-azirines and acyl chlorides

A simple and efficient regioselective synthesis of 4-oxazole-phosphine oxides 11 and -phosphonates 12 from 2H-azirine-phosphine oxides 1 and -phosphonates 6 is described. The key step for the synthesis of oxazoles 11 is a base-mediated ring closure of vinylogous α-aminophosphorus compounds derived from phosphine oxides 4 and from phosphonates 8. These derivatives 4 and 8 are obtained by reaction of functionalized azirines 1 and 6 with acyl chlorides 2 and subsequent acid-catalyzed ring opening of N-acylaziridine-phosphine oxides 3 and -phosphonates 7. Regioselective thermal ring cleavage of N-acylaziridine-phosphine oxides 3 leads α-chloro-β-(N-acylamido)-phosphine oxides 13 and their treatment with bases gives 5-oxazole-phosphine oxides 16.     

A novel approach to conformationally strained 2,2′-bipyridine thiacrown ethers and their chiral sulfoxides by sequential homo-coupling/DA-rDA reaction of 5,5′-bi-1,2,4-triazine-containing thiamacrocycles

The synthesis of conformationally strained 2,2′-bipyridine thiamacrocycles 5, 6, 9, 10 and their chiral sulfoxides 11-14 is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfide 3 with potassium cyanide and (2) Diels-Alder/retro Diels-Alder (DA-rDA) with 2,5-norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps. The crystal structure determinations of 4-6 and the theoretical calculations at DFT/B3LYP/6-311G^∗∗ level were conducted thus establishing conformational preferences of the target thiamacrocycles     

Biomimetic syntheses of ineleganolide and sinulochmodin C from 5-episinuleptolide via sequences of transannular Michael reactions

Treatment of a solution of the macrocyclic norcembranoid 7 with lithium hexamethyldisilazide in THF at −78 °C to 0 °C, leads to the polycyclic norcembranoids ineleganolide 1 and sinulochmodin C (2) (65%), which are found in the corals Sinularia inelegans and Sinularia lochmodes, respectively. The conversions are believed to be biomimetic, and occur by successive transannular Michael reactions in 7. Under different temperature conditions the novel polycycle 30 is the main product, alongside small quantities of 1 and 2. The polycycle 30 is possibly produced from ineleganolide 1, following a reverse oxy-Michael reaction and two successive aldol reactions. The significance of the synthesis of ineleganolide 1, sinulochmodin C (2) and the structure 30 from 5-episinuleptolide 7, to the likely biosynthesis of the related norcembranoids scabrolide A (3), scabrolide B (4) and horiolide 31 found in Sinularia sp. is discussed.     

Thermal decomposition of the tert-butyl perester of thymidine-5′-carboxylic acid. Formation and fate of the pseudo-C4′ radical

Thermal decomposition of the tert-butyl perester of thymidine-5′-carboxylic acid 1 carried out at 85 °C in different solvents affords the tert-butylacetal 4a, deriving from in cage decomposition, and pseudo C4′ radicals 2. Radicals 2 can be reduced to 5 by hydrogen atom abstraction from thiol (thiophenol or glutathione) or THF, or can be oxidized to cations 8 by dioxygen or perester 1 itself. Cations 8 are stereoselectively trapped by the nucleophilic solvent (tert-butanol, methanol, water) to give acetals 4a-c.     

Rapid syntheses of (±)-pterocarpans and isoflavones via the gold-catalyzed annulation of aldehydes and alkynes

(±)-Pterocarpan and analogues (4a-c) have been synthesized efficiently via the annulation of salicylaldehydes (1a, 1b and 1c) and o-methoxymethoxylphenylacetylene (2a), followed by a one-pot reduction and acidic cyclization of the ketones (3a-c). In addition, isoflavone derivatives (5a-c) have been synthesized rapidly, in two steps, via the annulation of salicylaldehyde (1a) and arylacetylenes (2b, 2c and 2d), followed by IBX/DMSO oxidation of the isoflavanones (3d, 3e and 3f).     

Syntheses, structures, luminescence, and magnetism of four 3D lanthanide 5-sulfosalicylates

Four 3D lanthanide(III) complexes with 5-sulfosalicylic acid (H₃SSA) as bridging ligands, Ln(SSA)(H₂O)₂ [Ln=Ce(III) (1), Pr(III) (2), Nd(III) (3) and Dy(III) (4)], have been synthesized and characterized by elemental analysis, IR, XRD and single-crystal X-ray diffraction. X-ray structural analysis reveals that isostructral complexes 1-4 possess 3D structures with 4⁶6⁴ topology. Complexes 1 and 2 exhibit broad intraligand fluorescent emission bands. Complexes 3 and 4 not only display intraligand fluorescent emission bands, but also present Nd(III) characteristic emission in the near-IR region and sensitized luminescence of Dy(III) ions in the visible region, respectively. Variable-temperature magnetic susceptibility measurements of 2-4 have been studied over the temperature range of 4-300 K.     

Synthesis of (3′R,5′S)-3′-hydroxycotinine using 1,3-dipolar cycloaddition of a nitrone

To synthesize (3′R,5′S)-3′-hydroxycotinine [(+)-1], the main metabolite of nicotine (2), cycloaddition of C-(3-pyridyl)nitrones 3a, 3c, and 15 with (2R)- and (2S)-N-(acryloyl)bornane-10,2-sultam [(2R)- and (2S)-8] was examined. Among them, l-gulose-derived nitrone 15 underwent stereoselective cycloaddition with (2S)-8 to afford cycloadduct 16, which was elaborated to (+)-1.