Regioselective Synthesis of 1,8-Naphthyridinone-Annulated Oxygen and Sulfur Heterocycles by Tri-n-butyl Tinhydride–Mediated Aryl Radical Cyclization

The tin hydride–mediated cyclizations of a number of ethers, sulfides, and sulfones under mild, neutral conditions have been investigated. While the 2-bromobenzyloxy ethers were prepared in 62–65% yields by the alkylation of 4-hydroxy-1-phenyl-1,8-naphthyridin-2(1H)-one with 2-bromobenzyl bromides in refluxing acetone in the presence of anhydrous potassium carbonate, the sulfides were derived from 4-mercapto-1-phenyl-1,8-naphthyridin-2(1H)-one and 2-bromobenzyl bromides in 82–84% yields by a phase-transfer catalysis (PTC) reaction. The corresponding sulfones were prepared by treatment of the sulfides with m-CPBA in refluxing dichloromethane. The ethers, sulfides, and the sulfones were treated with ⁿ Bu₃SnH-AIBN to give regioselectively 1,8-naphthyridinone-annulated oxygen and sulfur heterocycles in 70–78% yields.     

Synthesis of Pyrimidine Annelated Heterocycles [1]. Regioselective Heterocyclization of 6-Cyclopent-2-enyl-5-hydroxy-1,3-dimethyl-pyrimidine-2,4( 1H, 3H)-dione and 5-Cyclopent-2-enyl-6-hydroxy-1,3-dimethylpyrimidine-2,4( 1H, 3H)-dione

Summary. Two hitherto unreported pyrimidine annelated heterocycles were synthesized from 6-cyclopent-2-enyl-5-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione and 5-cyclopent-2-enyl-6-hydroxy-1,3-dimethylpyrimidine-2,4(1H,3H)-dione by reaction with pyridine hydrotribromide or hexamethylenetetramine hydrotribromide. The first one was also obtained by reaction with concentrated sulfuric acid.Received October 28, 2002; accepted October 30, 2002 Published online June 2, 2003     

Thermal and spectral properties of some anhydrous and hydrated rare earth hydrazinecarboxylates

Thermal investigations of two novel coordination compounds, potential precursor of copper sulfides, namely [Cu₂(S₂O₃)₂(NH₃)₄]·₅H2_O and Na₂[Cu₄(S₂O₃)₅(NH₃)₈]·₂H₂O were performed either in solid state (static air atmosphere), as well as in reaction medium. During both decompositions, Cu²⁺ reduction occurs. In solid state decomposition, a mixture containing sulfides and sulfates is observed. In the reaction medium, CuS_y compounds with sulfur content y (0.66<y<1) dependent on thiosulfate concentration are obtained. This revised version was published online in July 2006 with corrections to the Cover Date.     

All-trans-N-retinylidenetryptamine Schiff base in surfactant solubilized water pools in heptane—a fluorescence study

All-trns-N-retinylidenetryptamine Schiff base was incorporated into aerosol-OT (AOT, sodium bis(2-ethylhexyl)sulphosuccinate)/heptane reverse micelles. This micellar system was used as a model to study the retinal-tryptophan interactions in retinal proteins. The retinylidene Schiff base remains stable in the presence of reverse micelle-solubilized water pools. Partition coefficient and microviscosity measurements show that the Schiff base is located in the micellar interphase. The results are discussed in terms of the interaction between the retinylidene chromophore and the active site environment of rhodopsin and bacteriorhodopsin. In the present model, the quencher and emitting units are covalently attached, and are separated by two carbon spacer units. The fluorescence emission data obtained for the micelle-intercalated Schiff base chromophore are compared with the fluorescence of the native protein and intermediates in the photochemical cycle of bacteriofhodopsin. A comparison of the data obtained for tryptamine and the Schiff base with the results available for bacteriorhodopsin and bacterioopsin reveals that there is a large degree of quenching on intercalation of the retinylidene chromophore in the vicinity of the fluorophore. Evidence provided by this model suggests that energy transfer to retinal can occur from tryptophan residues located in the retinal pocket in the native protein. Thus the retinylidene unit can act as a quencher of the energy of tryptophan, the nature and extent of which may depend on the conformation and relative orientation of the protein-bound fluorophore.     

Chemical reaction studies in CH4/Ar and CH4/N2 gas mixtures of a dielectric barrier discharge

Chemical reactions in a dielectric barrier discharge at medium pressure of 250-300 mbar have been studied in CH(4)/Ar and CH(4)/N(2) gas mixtures by means of mass spectrometry. The main reaction scheme is production of H(2) by fragmentation of CH(4), but also production of higher order hydrocarbon molecules such as C(n)H(m) with n up to 9 including formation of different functional CN groups is observed. Formation of C(2)H(2), C(2)H(4), and C(2)H(6) molecules has been investigated in some detail. Significant differences are noted in comparison to a theoretical estimate.     

A family of mixed-ligand oxovanadium(V) complexes incorporating tridentate ONO donor hydrazone ligands derived from acetylhydrazide and 2-hydroxybenzaldehyde/2-hydroxyacetophenone

In the title family the tridentate ONO donor ligands are the fully deprotonated forms of acetylhydrazones of 2-hydroxybenzaldehyde (H₂L¹) and 2-hydroxyacetophenone (H₂L²) (general abbreviation H₂L), while bidentate mononegative OO donor ligands are the deprotonated salicylaldehyde (Hsal), vanillin (Hvan) and monodeprotonated 1,2-ethanediol (H₂ed) (general abbreviation HB). The reaction of V^IVO(acac)₂ with H₂L and Hsal or Hvan in equimolar ratio in MeOH afforded the complexes of the type [V^VO(L)(B)], (1)–(4). The reaction of V^IVO(acac)₂ with H₂L¹ (in an equimolar ratio) and an excess of H₂ed in MeOH yielded the complex [V^VO(L¹)(Hed)], (5) but the similar reaction with H₂L² ligand failed to produce such a type of complex. Complexes have been characterized by elemental analyses and by i.r., n.m.r. and u.v.-vis. spectroscopies. All the complexes are diamagnetic and display only LMCT bands. ¹H-n.m.r. spectral data indicate that complexes (1)–(4) exist in two isomeric forms [(1A), (1B); (2A), (2B); (3A), (3B) and (4A), (4B)] in different ratios in CDCI₃ solution. Complexes (1)–(4) display a quasi-reversible one electron reduction peak in the −0.06 to +0.05 V versuss.c.e. region in CH₂CI₂ solution and (5) displays an irreversible reduction peak at −0.46 V versuss.c.e. in DMF solution. The trend in the redox potential values has been correlated with the basicity of both the primary and auxiliary ligands.     

Regioselective Synthesis of Thiopyrano[3,2‐c][1]benzothiopyran‐5(2H)‐one and Thieno[3,2‐c][1]benzothiopyran‐4(2H)‐one

4‐Mercaptothiocoumarin was alkylated with different propargylic and allylic halides under phase‐transfer‐catalyzed conditions in the presence of tetrabutylammonium bromide (TBAB) or benzyl triethylammonium chloride (BTEAC) catalyst in dichloromethane–aqueous NaOH solution (1%) at room temperature. These 4‐thiopropynyl and thioallyl thiocoumarins were then refluxed in chlorobenzene and quinoline to give thiopyrano[3,2‐c][1]benzothiopyran‐5(2H)‐one and thiopyrano[3,2‐c][1]benzothiopyran‐4‐one respectively.     

Regioselective Synthesis of Benzofuran‐Annulated Six‐Membered Sulfur Heterocycles by Aryl Radical Cyclization

The tin hydride–mediated cyclization of a number of sulfides and sulfones under mild and neutral conditions has been investigated. The sulfides were in turn derived from 3(2H) benzothiofuranone and 2‐bromobenzyl bromides by phase‐transfer‐catalyzed reaction, and the corresponding sulfones were prepared by treatment of the corresponding sulfides with m‐CPBA at room temperature. The sulfides and sulfones were then reacted with ⁿ Bu₃SnH‐AIBN to afford regioselectively benzofuran‐annulated six‐membered sulfur heterocycles.     

Cyclisation of Ortho -Cyclohexenyl Phenols via Epoxidation #

A number of ortho -cyclohexenyl phenols 2(a–i) have been cyclised by treatment with one equivalent of m-chloroper-oxybenzoic acid in refluxing benzene for 4 h to furnish linearly fused 1-hydroxy-1,2,3,4,4a,9a-hexahydrodibenzofurans 3(a–i) (70–80%) and bicyclic 3-hydroxy-1,3-ethanochromans 4(a–f) (10–20%). Products 3(a–i) were oxidised with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (excess) in refluxing dry xylene for 6 h to give 2,3-dihydrodibenzofuran-1 (2H)-ones 6(a–i) (85–95%).