Synthesis and structure of 1,3-bis(hydroxysilyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane

Trans-silylation reactions of (Me₃Si)₂NH with PhRSiCl₂ (R = Me, Ph) gave HN(SiMePhCl)₂ (1) or ClMePhSiNHSiPh₂Cl (2). The treatment of 1,3-dichlorodisilazane (1 or 2) with an equimolar amount of n-BuLi led to the formation of 1,3-bis(chloro-silyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane (ClSiMePh)₂(NSiMePh)₂ (3) or (ClSiPh₂)₂(NSiMePh)₂ (4), which was allowed to hydrolyze to form 1,3-bis(hydroxysilyl)-2,4-dimethyl-2,4-diphenylcyclodisilazane (HOSiMePh)₂(NSiMePh)₂ (5) or (HOSiPh₂)₂(NSiMePh)₂ (6), respectively. The cyclodisilazane monomers were characterized by elemental analysis, NMR and IR spectroscopy. Compound 3 was obtained as a 4:6 cis/trans mixture while 4 adopted trans-structure considering the hindrance of pendent groups. In addition, the molecular structures of trans-5 and trans-6 were determined by X-ray crystallographic analysis and discussed in detail.     

2(H)-1,4-Oxazin-2-ones as ambident azadienes

3,5-Dichloro-6-phenyl-2(H)-1,4-oxazin-2-one 3, 5-chloro-3,6-dimethyl-2(H)-1,4-oxazin-2-one 4, 5-chloro-6-methyl-3-phenyl-2(H)-1,4-oxazin-2-one 5 and 5-chloro-3,6-diphenyl-2(H)-1,4-oxazin-2-one 7, are ambident azadienes reacting efficiently and selectively with both electron rich and electron poor dienophiles.     

The first synthesis and X-ray structures of polyfluorinated 1,2-, 2,3- and 2,4a-dihydro-1,3-diazafluorenes

Acetic acid-catalyzed condensation of 2-amino-3-(1-imino-2,2,2-trifluoroethyl)-1,1,4,5,6,7-hexafluoroindene (1b) with acetone and cyclopentanone gives 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene (2a) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-2,3-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3a) together with small amounts of 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene (2b) and 5,6,7,8,9,9-hexafluoro-4-trifluoromethyl-1,2-dihydro-1,3-diazafluorene-2-spiro-1′-cyclopentane (3b), respectively. When acted upon by (CH₃)₂SO₄ compounds 2, 3 were converted into corresponding fluorine-containing 1-methyl-1,2-dihydro-1,3-diazafluorenes 6, 7. 4a-Chloro-5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-2,4a-dihydro-1,3-diazafluorene (8) has been synthesized by the interaction of compound 2 with SOCl₂. Solution of compound 2 as well as 8 in CF₃SO₃H-CD₂Cl₂ generated 5,6,7,8,9,9-hexafluoro-2,2-dimethyl-4-trifluoromethyl-1,2,3,4-tetrahydro-1,3-diazafluorene-4-yl cation (2c). The structures of compounds 2, 3, 6-8 have been determined by single crystal X-ray diffraction.     

Novel titana-2,4-cyclopentadienes by 1,1-alkylboration

Bis(trimethylsilyl)amino-(2,2,5,5-tetramethyl-1,2,5-azadisila-cyclopent-1-yl)-titanium dichloride (3) and bis(2,2,5,5-tetramethyl-1,2,5-azadisila-cyclopent-1-yl)-titanium dichloride (4) were prepared and converted into the di(1-alkynyl)titanium derivatives, (Me₃Si)₂N[(CH₂Me₂Si)₂N]Ti(CCR)₂ (5) and [(CH₂Me₂Si)₂N]₂Ti(CCR)₂ (6) [R=Me (a), Ph (b), SiMe₃ (c)]. The reaction of 5a and 5b with trialkylboranes such as Et₃B leads almost quantitatively to titana-2,4-cyclopentadienes 7a and 7b, in which a diethylboryl group functions as a substituent in 3-position. In the same manner, 6b reacts with Et₃B or Pr₃B to titana-2,4-cyclopentadienes 8b or 9b, respectively. It is proposed that these reactions proceed by 1,1-alkylboration. Compound 5c also reacts with Et₃B, however, a complex mixture was obtained. All products were characterised by ¹H-, ¹¹B-, ¹³C-, ¹⁵N- and ²⁹Si-NMR spectroscopy.     

An efficient electrochemical method for a unique synthesis of new derivatives of 7H-thiazolo[3,2-b]-1,2,4-triazin-7-one

The electrochemical oxidation of catechols (1a-c) has been studied in the presence of 6-methyl-1,2,4-triazine-3-thion-5-one 3 in aqueous sodium acetate, using cyclic voltammetry and controlled-potential coulometry. A plausible mechanism for the oxidation of catechols and their reaction with 3 is presented. All the catechol derivatives (1a-c) were converted into 7H-thiazolo[3,2-b]-1,2,4-triazin-7-one derivatives (6a-c) through a Michael-type addition reaction of 3 to anodically generated o-quinones. The electrochemical syntheses of 6a-c were successfully performed in one pot in an undivided cell using an environmentally friendly method with high atomic economy.     

Comparative studies for selective deprotection of the N-arylideneamino moiety from heterocyclic amides: kinetic and theoretical studies. Part 2

4-Benzylideneamino-1,2,4-triazine-3,5(2H,4H)-diones (2-5), 6-styryl-1,2,4-triazine-3,5(2H,4H)-dione (6), and 6-styryl-2,3-dihydro-3-thioxo-1,2,4-triazin-5(4H)-one (7) were synthesized and pyrolyzed in the gas phase. The kinetic effect of changing the substituent on the triazine ring from hydrogen to methyl, phenyl, and styryl was measured. Analyses of the pyrolyzates of 2-5 showed the elimination products to be benzonitrile and the triazine fragment, while the pyrolyzates of 6 and 7 reveal the formation of cis- and trans-cinnamonitriles. Theoretical study of the pyrolysis reactions of 2-5 using an ab initio SCF method was investigated.     

First cross-coupling reactions on halogenated 1H-1,2,4-triazole nucleosides

The halogenated 1H-1,2,4-triazole glycosides 6-10 were synthesized by BF₃-activated glycosylation of 3(5)-chloro-1,2,4-triazole (2), 3,5-dichloro-1,2,4-triazole (3), 3,5-dibromo-1,2,4-triazole (4), and 3(5)-bromo-5(3)-chloro-1,2,4-triazole (5) with 1,2,3,4-tetra-O-pivaloyl-β-d-xylopyranose (1). The β-anomeric major products 3-chloro-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (6β), 3,5-dichloro-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (7β), and 3,5-dibromo-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (8β) were used as starting materials for transition metal catalyzed C-C-coupling reactions. Arylations of the triazole ring of 7β, and 8β were successful in 5-position with phenylboronic acid, 4-vinylphenylboronic acid, and 4-methoxyphenylboronic acid, respectively, under Suzuki cross-coupling conditions (products 11-17). Moreover, a Cu-catalyzed perfluoroalkylation of 8β is reported with 1-iodo-perfluorohexane yielding 3-perfluorohexyl-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazole (18). Compound 18 was depivaloylated to the trihydroxy derivative 19. The copper-mediated reaction of 8β with Rupert's reagent gave the bis(3-bromo-1-(2,3,4-tri-O-pivaloyl-β-d-xylopyranosyl)-1,2,4-triazol-5-yl) (20).     

Synthesis of novel 5-amino-1-aroylpyrazoles

A series of 5-amino-1-aroylpyrazoles 3 are synthesized directly by the reaction of β-aminocrotononitrile 1 with some structures containing the hydrazine moiety (X-NHNH₂) 2 by refluxing ethanol in presence of sodium acetate. When semicarbazide 3i was used (X = CONH₂), the reaction afforded the unexpected 7-aminopyrazolo[1,5-a]pyrimidine 4.     

Penilactones A and B, two novel polyketides from Antarctic deep-sea derived fungus Penicillium crustosum PRB-2

Two highly oxygenated polyketides, penilactones A and B (1 and 2), containing a new carbon skeleton formed from two 3,5-dimethyl-2,4-diol-acetophenone units and a γ-butyrolactone moiety, together with five known compounds (3-7) were isolated from an Antarctic deep-sea derived fungus Penicillium crustosum PRB-2. Penilactones A and B possess antipodal absolute stereochemistries. Their structures were elucidated by spectroscopic methods, and their absolute configurations were assigned by single-crystal X-ray diffraction and CD analyses. A plausible biogenetic pathway for 1-2 is proposed.     

Synthesis, photophysical and photochemical properties of highly soluble phthalocyanines substituted with four 3,5-dimethylpyrazole-1-methoxy groups

The synthesis and characterization of new peripherally tetra-3,5-dimethylpyrazole-1-methoxy substituted metal-free (4), zinc (5), nickel (6), cobalt (7), copper (8) and lead (9) phthalocyanines are described for the first time in this study. The photophysical (fluorescence quantum yields and fluorescence lifetimes) and photochemical (photodegradation and singlet oxygen quantum yields) properties of metal-free (4), zinc (5) and lead (9) phthalocyanines are studied in dimethylsulfoxide (DMSO). Nickel (6), cobalt (7) and copper (8) phthalocyanines (6-8) did not evaluate for this purpose due to transition metal and paramagnetic behavior of central metals in the phthalocyanine cavity. The fluorescence quenching behavior of metal-free (4), zinc (5) and lead (9) phthalocyanines are also investigated. The fluorescence emissions of these phthalocyanines are effectively quenched by 1,4-benzoquinone in DMSO.     

New cyclic zwitterionic building blocks for the synthesis of piperidine-2,4-dione and pyridine-2-one compounds

In this Letter we describe the synthesis of new chiral cyclic zwitterionic pyridin-2-one compounds 5a,b via an intramolecular ring-closure reaction of a stabilize amide sulfur ylide 4a,b derived from (R)-(−)-2-phenylglycinol and (R)-(+)-phenylethylamine in a high yield. In addition, we proved the utility of 5a,b to produce piperidine-2,4-dione 6a,b and pyridine-2-one 7a,b depending on the reaction conditions.     

Vinyl-addition polymerization of norbornene catalyzed by (pyrazol-1-ylmethyl)pyridine divalent iron, cobalt and nickel complexes

Complexes of 2-((3,5-dimethyl)-1H-pyrazol-1-ylmethyl)pyridine (L1), 2-((3,5-ditert-butyl-1H-pyrazol-1-yl)methyl)pyridine (L2), 2-((3,5-diphenyl)-1H-pyrazol-1-yl)methyl)pyridine (L3), 2-((3,5-bis(trifluoromethyl)-1H-pyrazol-1-ylmethyl)pyridine (L4) and 2,6-bis(3,5-dimethyl-1H-pyrazol-1-yl)methyl)pyridine (L5) with cobalt(II), iron(II) and nickel(II), Ni(L1)Cl₂ (1), Co(L1)Cl₂ (2), Fe(L1)Cl₂ (3), Ni(L2)Cl₂ (4), Ni(L3)Cl₂ (5), Co(L3)Cl₂ (6), Fe(L3)Cl₂ (7), Ni(L4)Cl₂ (8) and Ni(L5)Cl₂ (9), were used as catalyst precursors to produce vinyl-addition type norbornene polymers. Both the identity of the metal center and nature of ligand affected the polymerization behaviour of the resultant catalysts. Nickel catalysts were generally more active than the corresponding iron and cobalt analogues. The polynorbornene produced have high molecular weights (0.5-2.1 × 10⁶ g/mol) and narrow molecular weight distributions. Analyses of polymer microstructure using NMR and IR spectroscopy confirmed the polymers produced to be vinyl-addition polynorbornene.     

Steroid and cembranoids from the Dongsha atoll soft coral Lobophytum sarcophytoides

A novel sterol, sarcophytosterol (1), and four new cembranoids, sarcophytolins A-D (2-5), have been isolated from the soft coral Lobophytum sarcophytoides along with four known metabolites 6-9. The relative structures of new metabolites were elucidated on the basis of extensive spectroscopic analyses and X-ray diffraction analysis of 1, and the absolute configurations of 1 and 5 were determined by Mosher’s method and CD spectrum, respectively. Compound 1 is a steroid possessing an unusual (20R,23R,24R)-23,24-dimethyl-20-hydroxy side chain. Compounds 3, 6, 8, and 9 were shown to exhibit cytotoxicity toward a limited panel of cancer cell lines. Furthermore, while 1 could effectively enhance the expression of the pro-inflammatory iNOS protein in LPS-stimulated RAW264.7 macrophage cells, compounds 2, 3, 5-7 and 9 were found to effectively inhibit the accumulation of the pro-inflammatory of iNOS.     

Guignardins A–F,spirodioxynaphthalenes from the endophytic fungus Guignardia sp. KcF8 as a new class of PTP1B and SIRT1 inhibitors

Six new guignardins A–F (1–6) were isolated from the cultures of endophytic fungus Guignardia sp. KcF8 derived of a mangrove plant Kandelia candel, along with three known analogues, palmarumycins C₁ (7), BG1 (8), and JC1 (9). Compounds 2, 3, 7, and 8 showed antimicrobial activities. Compounds 5–7 exhibited significant cytotoxicities against 10 human tumor cell lines. Compound 3 also displayed significant inhibitory activity against human protein tyrosine phosphatase 1B and histone deacetylase silent information regulator T1enzymes, two key targets for the treatment of diabetes. This is the first report on the anti-PTP1B and anti-SIRT1 activities of spirodioxynaphthalenes.     

Oxygen replacement by fluorine in carbonyl derivatives of perfluoroaromatic compounds and isomerization of perfluoroindan-1,3-dione to perfluoro-3-methylenephthalide under the action of HF/SbF5

When acted upon by HF/SbF₅ at 95 °C, carbonyl groups of perfluorinated acetophenone (10), 3,4-dihydronaphthalen-1(2H)-one (8), 2,3-dihydronaphthalene-1,4-dione (9), benzocyclobutenone (6), benzocyclobutenedione (7) and indan-1-one (1) are converted into difluoromethylene groups to give the corresponding perfluoroaromatic products. Perfluoroindan-2-one (5), under the same conditions, is transformed to bis(perfluoroindan-2-yl) ether (21). On heating with HF/SbF₅, perfluoroindan-1,3-dione (2) isomerizes into perfluoro-3-methylenephthalide (4) at 95 °C, and gives 4,5,6,7-tetrafluoro-3-trifluoromethyl-phthalide (14) at 130 °C. Compound 4 in the absence of a solvent dimerizes giving perfluorodispiro[phthalide-3,1′-cyclobutane-2′,3″-phthalide] (18), and when heated with SbF₅ at 130 °C, it is converted into perfluoro-3-methylphthalide (3). When acted upon by HF/SbF₅ at 95 °C, perfluorinated benzoic acid (12) and phthalic anhydride (13) give the corresponding products with trifluoromethyl groups.     

Fluorinated molecules relevant to conducting polymer research

The synthesis of versatile fluorine compounds for conducting polymer research on fluorinated materials is presented. 1,2,4,5-Tetrafluorobenzene was converted to 1,2,4,5-tetrafluorobenzaldehyde (1) and protected as an acetal. This gave the acetals 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)benzene (2a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)benzene (2b). Compounds 2a and 2b were converted into the semiprotected 2,3,5,6-tetrafluoroterephthaldehydes: 1,2,4,5-tetrafluoro-3-(1,3-dioxol-2-yl)-6-formylbenzene (3a) and 1,2,4,5-tetrafluoro-3-(5,5-dimethyl-1,3-dioxan-2-yl)-6-formylbenzene (3b). While 3a was easily deprotected to give 2,3,5,6-tetrafluoroterephthaldehyde (4) compound 3b proved very resilient to hydrolysis and gave a 1:1 mixture of 4 and 1,2,4,5-tetrafluoro-3,6-bis(5,5-dimethyl-1,3-dioxan-2-yl)benzene (5). Compound 4 was reduced to 1,2,4,5-tetrafluoro-3,6-dihydroxymethylbenzene (6) and converted into 1,2,4,5-tetrafluoro-3,6-dibromomethylbenzene (7). Compound 7 was finally converted into 1,2,4,5-tetrafluoro-3,6-bis(diethylphosponylmethyl)benzene (8). Compounds 4 and 8 are versatile fluorinated molecules that can be used to replace their hydrogen counterparts in many molecules and materials. To illustrate this compounds 4 and 8 were oligomerised to give partially fluorinated polyphenylenevinylene (9).     

Studies on organophosphorus compounds: reactions of benzosuberones with 2,4-bis(p-methoxyphenyl)-1,3,2,4-dithiadiphosphetane-2,4-disulfide (Lawesson's reagent)

6-Arylidene-3-methyl-6,7,8,9-tetrahydro-5H-benzo[a]cyclohepten-5-ones (2a-h), obtained by the condensation of 3-methylbenzocyclohepten-5-one 1 with appropriate aromatic aldehydes, on reaction with Lawesson's reagent in xylene yielded phosphorus containing compounds 3a-h. A number of these compounds showed promising anti-inflammatory activity.     

Synthesis and characterization of 3,5-lutidinyl chalcogen and -dichalcogen compounds: X-ray crystal structure of bis(3,5-dimethyl-2-pyridyl) diselenide and 2,6-bis(selenomethyl)-3,5-lutidine

The synthesis of 3,5-lutidinyl chalcogen and -dichalcogen compounds has been described by a method involving selective mono- and dilithiation of 3,5-lutidine (1) ring. The selective mono- and dilithiation of 1 has been achieved by reacting BF₃-complexed 3,5-lutidine (2) with 1 and 2 equiv of LTMP/LDA respectively. The subsequent insertion of elemental selenium followed by aerial oxidation or quenching with iodomethane leads to the formation of bis(3,5-dimethyl-2-pyridyl) diselenide (5) and 2,6-bis(selenomethyl)-3,5-lutidine (7) respectively. In addition, sequential incorporation of sulfur and selenium atom in the same lutidine ring has been reported for the first time. Single-crystal X-ray studies of (5), having a rare C-Se-Se-C torsion angle of 180°(4), and (7) have also been reported.     

Reaction of selenofenchone with propiolic acid: first instance of Wagner-Meerwein rearrangement in selone

The reaction of selenofenchone (3a) with propiolic acid in refluxing chloroform produced selenodioxenone (4) along with rearranged product (5b), while 5b was obtained in almost quantitative yield under solvent-free conditions. In the presence of Lewis acid, selenofenchone 3a reacted with methyl propiolate to afford corresponding rearranged adduct (7).     

Synthesis of 12-deoxyroyleanone, cryptoquinone, 11,14-dihydroxy-8,11,13-abietatrien-7-one, and related derivatives from dehydroabietic acid

Naturally occurring abietane quinones and hydroquinone, namely, 12-deoxyroyleanone (1a), cryptoquinone (4a), and 11,14-dihydroxyabieta-8,11,13-trien-7-one (5a), together with the epimers of tryptoquinones D (2) and F (3), were first synthesized from dehydroabietic acid (6).