A study of the physico-chemical properties of 1,3,5-trihydroxy-1,3,5-triazin-2,4,6[1H,3H,5H]-trione

Acetyl (Ia) and pivaloyl (Ib) triesters of the 1N,3N,5N-trihydroxy-1,3,5-triazin-2,4,6[1H,3H,5H]-trione (I) were synthesised. The spectrophotometric and potentiometric investigation of I revealed a weak acidic properties of triprotonic acid (pK_a1=5.23, pK_a2=6.32, and pK_a3=7.93). The MS and TGA analyses of I indicated on hydroxyisocyanate as possible degradation product. The chelating ability of I with Fe(III)-ion was preliminary explored. IR measurements of aqueous solutions of I in the presence of Fe(III) ion showed the possible chelating ability of all hydroxamic moieties. The chemical structures and properties of investigated compounds were derived from the results of IR, ¹H and ¹³C NMR, UV and MS spectrometric data, as well as thermogravimetric and potentiometric analysis.     

Regioselective synthesis of 1H,3H,6H[2]benzopyrano[4,3-d]pyrimidine-2,4-diones and 12H-benzopyrano[3,2-c][1]benzopyran-5-ones by radical cyclization

5-Hydroxy uracils or 4-hydroxy[1]benzopyran-2-ones were refluxed with 2-bromobenzyl bromides in acetone in the presence of anhydrous potassium carbonate to afford a number of 5-(2′-bromobenzyloxy) pyrimidine-2,4-dione (80-92%) or 4-(2′-bromobenzyloxy) benzopyran-7-ones (70-82%) respectively. These were then refluxed with tri-n-butyltin chloride and sodium cyanoborohydride in the presence of a catalytic amount of azobisisobutyronitrile (AIBN) for 3-4 h to give 1H,3H,6H [2]benzopyrano[4,3-d]pyrimidine-2,4-diones (75-85%) or 12H-benzopyrano[3,2-c][1]benzopyran-5-ones (70-85%) respectively.     

Di(1H,1H,2H,2H-perfluorooctyl)-dibenzo-18-crown-6: A “light fluorous” recyclable phase transfer catalyst

A series of dibenzo-18-crown-6 lariat ethers containing two C₇H₁₅ (11), (CH₂)₂C₆F₁₃ (14), (CH₂)₂C₈F₁₇ (15), NHC₇H₁₅ (18) and NHCH₂C₆F₁₃ (19) sidearms were prepared and the single crystal X-ray structure of cis-4,4′-di(1H,1H,2H,2H-perfluorodecyl)-dibenzo-18-crown-6 (15a) is reported. The “light fluorous” dibenzo-18-crown-6 ether (14) has emerged as a stable and robust PTC catalyst, which can be recycled efficiently by fluorous solid-phase extraction, and gives better PTC catalytic activity compared to the parent, non-fluorinated PTC catalyst, dibenzo-18-crown-6, and the alkylated derivative (11) in aliphatic and aromatic nucleophilic substitutions.     

Flash vacuum pyrolysis of 2,2-dioxo-1H,3H-pyrrolo[1,2-c]thiazoles and 2-vinyl-1H-pyrroles

The flash vacuum pyrolysis of new 1,1-dimethyl- and 1-methyl-1H,3H-pyrrolo[1,2-c]thiazole-2,2-dioxides gave penta-substituted 2-vinyl-1H-pyrroles via sigmatropic [1,8]-H shift of the corresponding azafulvenium methide intermediates. In some cases these 1H-pyrroles underwent rearrangement to 2-allyl-1H-pyrroles. Di-substituted 2-vinylpyrroles have also been prepared and their reactivity studied. Under FVP N-benzyl-pyrrol-2-ylpropenoates were converted into 3H-pyrrolizin-3-ones. On the other hand, microwave-assisted reaction of 1-benzyl-2-vinyl-1H-pyrrole gave a 4,5,6,7-tetrahydro-1H-indole derivative.     

Rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones to furo[3,4-c]quinoline-3,4(1H,5H)-diones

Thermally assisted base-catalyzed rearrangement of furo[2,3-c]quinoline-2,4(3aH,5H)-diones 1 to the corresponding furo[3,4-c]quinoline-3,4(1H,5H)-diones 2 is reported, and a mechanism of the transformation is proposed.     

The direct arylation of 1,3,5-triazin-2,4(1H,3H)-dione

Direct introduction of non-activated arenes to 1,3,5-triazin-2,4(1H,3H)-dione in the presence of AlCl₃ is described.     

A general approach toward Janus diones: synthesis of dicyclopenta[b,g]naphthalene-1,3,6,8(2H,7H)-tetraone

A general approach toward Janus diones involving the reaction of pyromellitic or naphthalenetetracarboxylic dianhydrides with ethyl(triphenylphosphoranylidene)acetate and subsequent rearrangement of the products is described. This approach allows avoiding the formation of poorly soluble intermediates, in which purity cannot be effectively controlled. Dicyclopenta[b,g]naphthalene-1,3,6,8(2H,7H)-tetraone 3, a promising precursor of molecular and polymeric advanced materials is described.     

Reductive opening of 1H,3H-benzo[de]isochromene: synthesis of 1,8-difunctionalised naphthalenes

The lithiation of 1H,3H-benzo[de]isochromene (6) with lithium and a catalytic amount of 4,4′-di-tert-butylbiphenyl (DTBB, 5% molar) in THF at −50 °C gives dianionic intermediate 7, which by reaction with different electrophiles {H₂O, D₂O, ^tBuCHO, PhCHO, Me₂CO, (CH₃CH₂)₂CO, [CH₃(CH₂)₄]₂CO, (CH₂)₅CO, (CH₂)₇CO, (−)-menthone} at the same temperature followed by hydrolysis leads to functionalised alcohols 8. If after addition of a carbonyl compound as the first electrophile [^tBuCHO, (CH₂)₅CO, (−)-menthone], the resulting dialcoholate 9 is allowed to react at 0 °C, a second lithiation takes place to give intermediate 10 which by reaction with a second electrophile [H₂O, ^tBuCHO, (CH₂)₅CO, CO₂], yields, after hydrolysis, 1,8-difunctionalised naphthalenes 11. Cyclization under acidic conditions of diols 8e-i gives oxygen-containing eight-membered heterocycles, which are homologous to the starting material 6.     

Stereoselective reductions of N-Boc-hexahydro-1H-indolin-5(6H)-ones

We report the divergent effects of a 3a-methyl and 3a-phenyl substituent on the chemoselectivity and stereoselectivity of reduction of the enamide moiety of N-Boc-hexahydro-1H-indolin-5(6H)-ones. Under ionic reduction conditions (triethylsilane/trifluoroacetic acid) the enamide group of 3a-methyl-N-Boc-hexahydro-1H-indolin-5(6H)-one was reduced to afford exclusively a cis ring-fused product. For the 3a-phenyl substituted analogue more forcing conditions (sodium cyanoborohydride at pH 2-2.5) were required and resulted in the selective reduction of the enamide group to give a trans ring-fused product as well as reduction of the ketone group.     

Solid-phase synthesis of 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-thiones and 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-ones

An efficient approach for the synthesis of 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-thiones and 3-alkyl-8-arylamino-1H-imidazo[4,5-g]quinazolin-2(3H)-ones on solid phase has been developed. The reaction conditions were readily amenable and the products were obtained in good yields and purities after their cleavage from the resin.     

Photochemistry of 3H-furo[3,4-c]pyrazoles and 3H-thieno[3,4-c]pyrazoles

The first examples of 3H-furo[3,4-c]pyrazoles and 3H-thieno[3,4-c]pyrazoles were prepared in an attempt to isolate examples of cyclopropane-fused thiophenes and furans. Adducts of acetylenic ketones and 2-diazopropane were reacted with 10-camphorsulfonic acid or phosphorus pentasulfide to produce the title compounds. Photolysis of these compounds did not give the cyclopropane-fused products rather an unreported photochemical fragmentation was observed.     

The rearrangement of 1H,1′H-spiro[quinoline-4,2′-quinoxaline]-2,3′ (3H,4′H)-diones – a new and efficient method for the synthesis of 4-(benzimidazol-2-yl)quinolin-2(1H)-ones

A new and highly efficient method for the synthesis of 4-(benzimidazol-2-yl)quinolin-2(1H)-ones via the rearrangement of spiroquinoxalinones in moderate-to-excellent yields has been developed. The rearrangement represents a facile approach to medicinally important biheterocyclic compounds. Compared to other methods, the present protocol has a number of advantages such as – cost-effectiveness, avoidance of difficult of access quinolin-2-one and benzimidazole derivatives as reaction partners, and easy accessibility of starting materials, making it a highly practical approach to access various 4-(benzimidazol-2-yl)quinolin-2(1H)-ones.     

Convenient synthesis and unusual reactivity of 2-oxo-2H,5H-pyrano[3,2-c]chromenes

The reaction of 4-oxo-4H-chromen-3-carbaldehydes with coumarin-4-acetic acids under the Perkin conditions follows an interesting pathway that involves aldol reaction and subsequent intramolecular lactonization to afford 2-oxo-2H,5H-pyrano[3,2-c]chromene skeleton. In contrast to chromone-3-carbaldehydes, the same reaction with chromone-2-carbaldehydes yielded only the aldol condensation product. The reaction was performed under thermal and microwave conditions. The reactivity of 2-oxo-2H,5H-pyrano[3,2-c]chromenes in water, alcohol and acetic acid was described.     

Synthesis of novel 2H,5H-dihydrofuran-3-yl ketones via ISNC reactions

Unique 1-[2H,5H-dihydrofur-3-yl]ketones have been synthesized from propargylic nitroethers via intramolecular cycloadditions involving silyl nitronates. Various substituent groups were placed on the 2 and 5 positions of the dihydrofuran rings. We examined the scope of the long-range coupling in proton NMR of the oxo-dihydrofuran products. The identities of the diastereomers resulting from the Michael addition/cycloaddition reactions were tentatively assigned for the first time. CAChe MNDO PM5 and CONFLEX programs were engaged to assist with the identification of these stereoisomers. The reaction times and conditions for these oxo-dihydrofurans were found to be different from that of the published dihydrofuranals, which led us to propose a different mechanism.     

Water mediated catalyst-free efficient domino synthesis of 9-(quinolin-2(1H)-one)-xanthene-1,8(5H,9H)-diones using parallel synthesizer

A facile and efficient method for the preparation of 3,4,6,7-tetrahydro-9-(1,2-dihydro-2-oxoquinolin-3-yl)-2H-xanthene-1,8(5H,9H)-diones from substituted 2-chloro-3-formylquinoline and 1,3-cyclohexanedione or dimedone in water at 90 °C using parallel synthesizer is reported. The present methodology offers a tandem-cascade methodology, high yield, and operational simplicity.     

Reductive electrochemical formation of 6H-dibenzo[b,d]pyran-6-one and 2-benzopyran-1(1H)-one

In the present Letter several carbolactones (oxidative products) are obtained under aprotic cathodic conditions in the preparative scaled electrolysis of 1,2-quinones in a divided electrochemical cell and in the presence of oxygen. When 9,10-phenanthrenequinone is reduced 6H-dibenzo[b,d]pyran-6-one and [1,1′-biphenyl]-2,2′-dicarboxylic acid are obtained as major products. In the reduction of 1,2-naphthoquinone, 2-benzopyran-1(1H)-one, and 2-(2-carboxyethenyl)-benzoic acid were formed as main products. The proposed mechanism to explain the formation of these and other products, that involves an electron-transfer reaction to the oxygen in air, is now discussed.     

Is samoquasine A indeed benzo[f]phthalazin-4(3H)-one? Unambiguous, straightforward synthesis of benzo[f]phthalazin-4(3H)-one and its regioisomer benzo[f]phthalazin-1(2H)-one

In search for the structural elucidation of samoquasine A, a natural product isolated from the seeds of Annona squamosa L., two benzo[f]phthalazinone isomers have been synthesized. The synthetic pathway followed to build up these skeletons is based on the combination of two Suzuki reactions on a pyridazinone precursor and a ring closure reaction via a condensation reaction. ¹H NMR data of the synthesized compound allowed to establish that the structure of the natural product samoquasine A is not benzo[f]phthalazin-4(3H)-one, as previously suggested.     

A novel ionic liquid mediated synthesis of 4(1H)-quinolones, 5H-thiazolo[3,2-a]pyrimidin-5-one and 4H-pyrimido[2,1-b]benzothiazol-4-ones

A new, convenient, environmentally benign two-step synthesis of 4(1H)-quinolones, 5H-thiazolo[3,2-a]pyrimidin-5-one and 4H-pyrimido[2,1-b]benzothiazol-4-ones have been developed by first condensing substituted arylamine/2-aminothiazole/2-aminobenzenethiazole with Meldrum’s acid and trimethylorthoformate in 1-butyl-3-methylimidazolium bromide at a moderate temperature to afford 5-{(substituted aryl/4-methylthiazolyl/substituted benzothiazolyl)methylene}-2,2-dimethyl-1,3-dioxane-4,6-dione. The resulting compounds upon cyclization in 1-butyl-3-methyl tetrafluoroborate/triflate at a moderate temperature gave the title compounds in excellent yields.     

One-pot synthesis of novel 1,2,6,7-tetrahydro-3H-pyrazolo[4,3-c]pyridine-3,4(5H)-diones

A facile synthesis of novel 1,2,6,7-tetrahydro-3H-pyrazolo[4,3-c]pyridine-3,4(5H)-diones has been achieved. The operationally simple procedure, using readily available intermediates, allows for rapid derivatisation of the pharmacophore with alkyl, aryl and heteroaryl substituents.