Reactions of Sulfanyl Chlorides with Thiocamphor and Thiofenchone: Wagner?Meerwein Rearrangement of an Intermediate Thiocarbonylium Ion

The reaction of sulfanyl and disulfanyl chlorides with thiocamphor ( 6 ) in the presence of Et₃N leads to unsymmetrical di‐ and trisulfanes, respectively (Schemes 2 and 4). A reaction mechanism via a thiocarbonylium ion, which is immediately deprotonated, is proposed. The formation of a minor product 10 in the absence of a base, resulting from a Wagner? Meerwein rearrangement, is an additional evidence for the intermediacy of a thiocarbonylium ion (Scheme 3). On the other hand, the non‐enolizable thiofenchone ( 13 ) reacts with sulfanyl chlorides in CH₂Cl₂/Et₃N to give exclusively products with a rearranged bicyclic skeleton (Scheme 5). A Wagner? Meerwein rearrangement of the intermediate thiocarbonylium ion is the key step. The structures of the products 10 and 14 , which have rearranged bicyclic systems, have been established by X‐ray crystallography.     

Regioselectivity of the 1,3‐Oxathiolane Formation in the Lewis Acid‐Catalyzed Reaction of Thioketones with Asymmetrically Substituted Oxiranes

The reactions of the aromatic thioketone 4,4′‐dimethoxythiobenzophenone ( 1 ) with three monosubstituted oxiranes 3a – c in the presence of BF₃⋅Et₂O or SnCl₄ in dry CH₂Cl₂ led to the corresponding 1 : 1 adducts, i.e., 1,3‐oxathiolanes 4a – b with R at C(5) and 8c with Ph at C(4). In addition, 1,3‐dioxolanes 7a and 7c , and the unexpected 1 : 2 adducts 6a – b were obtained (Scheme 2 and Table 1). In the case of the aliphatic, nonenolizable thioketone 1,1,3,3‐tetramethylindane‐2‐thione ( 2 ) and 3a – c with BF₃⋅Et₂O as catalyst, only 1 : 1 adducts, i.e. 1,3‐oxathiolanes 10a – b with R at C(5) and 11a – c with R or Ph at C(4), were formed (Scheme 6 and Table 2). In control experiments, the 1 : 1 adducts 4a and 4b were treated with 2‐methyloxirane ( 3a ) in the presence of BF₃⋅Et₂O to yield the 1 : 2 adduct 6a and 1 : 1 : 1 adduct 9 , respectively (Scheme 5). The structures of 6a , 8c , 10a , 11a , and 11c were confirmed by X‐ray crystallography (Figs. 1 – 5). The results described in the present paper show that alkyl and aryl substituents have significant influence upon the regioselectivity in the process of the ring opening of the complexed oxirane by the nucleophilic attack of the thiocarbonyl S‐atom: the preferred nucleophilic attack occurs at C(3) of alkyl‐substituted oxiranes (O−C(3) cleavage) but at C(2) of phenyloxirane (O−C(2) cleavage).     

Synthesis of 1,2,4,5,7,8-hexaoxonanes by iodine-catalyzed reactions of bis(1-hydroperoxycycloalkyl) peroxides with ketals

Iodine-catalyzed reactions of bis(1-hydroperoxycycloalkyl) peroxides with ketals give, via replacement of two alkoxy groups, the cyclic peroxides, 1,2,4,5,7,8-hexaoxonanes, in up to 82% yields. The cyclization is very sensitive to the solvent nature. Among MeCN, Et₂O, THF, CHCl₃, CH₂Cl₂, hexane, and MeOH, the best results were achieved with the first three solvents.     

Reactions of Stable α‐Chlorosulfanyl Chlorides with CS‐Functionalized Compounds

The smooth reaction of 3‐chloro‐3‐(chlorosulfanyl)‐2,2,4,4‐tetramethylcyclobutanone ( 3 ) with 3,4,5‐trisubstituted 2,3‐dihydro‐1H‐imidazole‐2‐thiones 8 and 2‐thiouracil ( 10 ) in CH₂Cl₂/Et₃N at room temperature yielded the corresponding disulfanes 9 and 11 (Scheme 2), respectively, via a nucleophilic substitution of Cl^? of the sulfanyl chloride by the S‐atom of the heterocyclic thione. The analogous reaction of 3‐cyclohexyl‐2,3‐dihydro‐4,5‐diphenyl‐1H‐imidazole‐2‐thione ( 8b ) and 10 with the chlorodisulfanyl derivative 16 led to the corresponding trisulfanes 17 and 18 (Scheme 4), respectively. On the other hand, the reaction of 3 and 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazole‐5(4H)‐thione ( 12 ) in CH₂Cl₂ gave only 4,4‐dimethyl‐2‐phenyl‐1,3‐thiazol‐5(4H)‐one ( 13 ) and the trithioorthoester derivative 14 , a bis‐disulfane, in low yield (Scheme 3). At ?78°, only bis(1‐chloro‐2,2,4,4‐tetramethyl‐3‐oxocyclobutyl)polysulfanes 15 were formed. Even at ?78°, a 1 : 2 mixture of 12 and 16 in CH₂Cl₂ reacted to give 13 and the symmetrical pentasulfane 19 in good yield (Scheme 5). The structures of 11, 14, 17 , and 18 have been established by X‐ray crystallography.     

Extraction and isolation of the One-electron Oxidized [(Zr6Be)Cl18]5− and [(Zr6Be)Cl18]4− Clusters from solid state precursors

One-electron oxidized zirconium chloride clusters were obtained from solid state precursors Rb₅Zr₆Cl₁₈B and K₃Zr₆Cl₁₅Be by dissolution in CH₃CN in the presence of Et₄NCl and isolated as the salts (Et₄N)₄Zr₆Cl₁₈B · 2 CH₃CN and (Et₄N)₅Zr₆Cl₁₈Be · 3 CH₃CN. (Et₄N)₄Zr₆Cl₁₈B · 2 CH₃CN crystallizes in the space group P1 (#2) with a = 12.329(5) Å, b = 12.657(6) Å, c = 13.136(8) Å, α = 118.28(4)°, β = 93.45(4)°, γ = 105.54(3)°, V = 1696(2) ų, and Z = 1. (Et₄N)₅Zr₆Cl₁₈Be · 3 CH₃CN was refined in the space group C2/c (# 15) with a = 24.166(11) Å, b = 13.265(6) Å, c = 25.86(2) Å, β = 104.21(4)°, V = 8037(7) ų, and Z = 4; the space group reflects the pseudo-symmetry of the crystal, the true symmetry of the structure is lower. The removal of one electron from the Zr? Zr bonding HOMO of both clusters results in cluster expansion of similar magnitude in both compounds. Moisture from the added Et₄NCl is the likely oxidant, but the possibility that acetonitrile may be reduced by [(Zr₆Be)Cl₁₈]^6? is not ruled out.     

Synthesis of 1‐Methyl‐6,10‐diphenylheptalene Derivatives

The reduction of heptalene diester 1 with diisobutylaluminium hydride (DIBAH) in THF gave a mixture of heptalene‐1,2‐dimethanol 2a and its double‐bond‐shift (DBS) isomer 2b (Scheme 3). Both products can be isolated by column chromatography on silica gel. The subsequent chlorination of 2a or 2b with PCl₅ in CH₂Cl₂ led to a mixture of 1,2‐bis(chloromethyl)heptalene 3a and its DBS isomer 3b . After a prolonged chromatographic separation, both products 3a and 3b were obtained in pure form. They crystallized smoothly from hexane/Et₂O 7 : 1 at low temperature, and their structures were determined by X‐ray crystal‐structure analysis (Figs. 1 and 2). The nucleophilic exchange of the Cl substituents of 3a or 3b by diphenylphosphino groups was easily achieved with excess of (diphenylphospino)lithium (=lithium diphenylphosphanide) in THF at 0° (Scheme 4). However, the purification of 4a / 4b was very difficult since these bis‐phosphines decomposed on column chromatography on silica gel and were converted mostly by oxidation by air to bis(phosphine oxides) 5a and 5b . Both 5a and 5b were also obtained in pure form by reaction of 3a or 3b with (diphenylphosphinyl)lithium (=lithium oxidodiphenylphospanide) in THF, followed by column chromatography on silica gel with Et₂O. Carboxaldehydes 7a and 7b were synthesized by a disproportionation reaction of the dimethanol mixture 2a / 2b with catalytic amounts of TsOH. The subsequent decarbonylation of both carboxaldehydes with tris(triphenylphosphine)rhodium(1+) chloride yielded heptalene 8 in a quantitative yield. The reaction of a thermal‐equilibrium mixture 3a / 3b with the borane adduct of (diphenylphosphino)lithium in THF at 0° gave 6a and 6b in yields of 5 and 15%, respectively (Scheme 4). However, heating 6a or 6b in the presence of 1,4‐diazabicyclo[2.2.2]octane (DABCO) in toluene, generated both bis‐phosphine 4a and its DBS isomer 4b which could not be separated. The attempt at a conversion of 3a or 3b into bis‐phosphines 4a or 4b by treatment with t‐BuLi and Ph₂PCl also failed completely. Thus, we returned to investigate the antipodes of the dimethanols 2a, 2b , and of 8 that can be separated on an HPLC Chiralcel‐OD column. The CD spectra of optically pure (M)‐ and (P)‐configurated heptalenes 2a, 2b , and 8 were measured (Figs. 4, 5, and 9).     

Aminierende,reduktive Kupplung aromatischer Aldehyde mit Tris(dialkylamino)methylvanandium (IV) zu N,N,N′,N′-Tetraaalkyl-1,2-diaryläthylendiaminen

Aminative Reductive Coupling of Aromatic Aldehydes to N,N,N′,N′-Tetraalkyl-1,2-diarylethylenediamines, Induced by Tris(dialkylamino)methylvanadium (IV) In a novel type of reaction, certain aromatic aldehydes (benzaldehyde, p-methoxybenzaldehyde, 1-naphthaldehyde, furan-2-carbaldehyde) and secondary amines are coupled to give N,N,N′,N′-tetraalkyl-1,2-diarylethylenediamines 1–6 . The reagents are tris(dialkylamino)methylvanadium(IV) compounds (cf. Eqn. 2). These are generated in situ either from isolable chlorotris(dialkylamino) vanadium(IV) (Eqn. 3), or preferably, from an Et₂O/pentane solution of VCl₄ which is treated sequentially with 3 equiv. of lithium dialkylamide, 1 equiv. of MeLi, and 0.8 equiv. of an aromatic aldehyde, to give the products 1–6 in a one-pot preparation (Scheme 2). The yields range from 14 to 54%. The diastereoisomeric mixtures (meso- and (±)-forms) obtained are separated by chromatography (Al₂O₃, petroleum ether/Et₂O/Et₃N), and the pure stereoisomers fully characterized. A mechanism of the reductive coupling induced by CH₃V (NR₂)₃ is proposed (Scheme 1).     

Synthesis of Imidazole Derivatives Using 2‐Unsubstituted 1H‐Imidazole 3‐Oxides

The reaction of 1,4,5‐trisubstituted 1H‐imidazole 3‐oxides 1 with Ac₂O in CH₂Cl₂ at 0 – 5° leads to the corresponding 1,3‐dihydro‐2H‐imidazol‐2‐ones 4 in good yields. In refluxing Ac₂O, the N‐oxides 1 are transformed to N‐acetylated 1,3‐dihydro‐2H‐imidazol‐2‐ones 5 . The proposed mechanisms for these reactions are analogous to those for N‐oxides of 6‐membered heterocycles (Scheme 2). A smooth synthesis of 1H‐imidazole‐2‐carbonitriles 2 starting with 1 is achieved by treatment with trimethylsilanecarbonitrile (Me₃SiCN) in CH₂Cl₂ at 0 – 5° (Scheme 3).     

Channel‐forming solvates of 6‐chloro‐2,5‐dihydroxypyridine and its solvent‐free tautomer 6‐chloro‐5‐hydroxy‐2‐pyridone

On crystallization from CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂, 6‐chloro‐5‐hydroxy‐2‐pyridone, C₅H₄ClNO₂, (I), undergoes a tautomeric rearrangement to 6‐chloro‐2,5‐dihydroxypyridine, (II). The resulting crystals, viz. 6‐chloro‐2,5‐dihydroxypyridine chloroform 0.125‐solvate, C₅H₄ClNO₂·0.125CHCl₃, (IIa), 6‐chloro‐2,5‐dihydroxypyridine carbon tetrachloride 0.125‐solvate, C₅H₄ClNO₂.·0.125CCl₄, (IIb), 6‐chloro‐2,5‐dihydroxypyridine 1,2‐dichloroethane solvate, C₅H₄ClNO₂·C₂H₄Cl₂, (IIc), and 6‐chloro‐2,5‐dihydroxypyridine 1,1,2,2‐tetrachloroethane solvate, C₅H₄ClNO₂·C₂H₂Cl₄, (IId), have I4₁/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent‐free crystals with P2₁/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion‐related molecules form R²₂(8) dimers via pairs of N—H...O hydrogen bonds. The dimers are linked by O—H...O hydrogen bonds into R⁴₆(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel‐containing pyridine solvate crystals, viz. (IIa)–(IId), two independent host molecules form an R²₂(8) dimer via a pair of O—H...N hydrogen bonds. One molecule is further linked by O—H...O hydrogen bonds to two 4₁ screw‐related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O—H...O hydrogen bonded to two related equivalents to form tetrameric R⁴₄(28) rings. The dimers are π–π stacked with inversion‐related dimers, which in turn stack the R⁴₄(28) rings along c to form continuous solvent‐accessible channels. CHCl₃, CCl₄, CH₂ClCH₂Cl and CHCl₂CHCl₂ solvent molecules are able to occupy these channels but are disordered by virtue of the site symmetry within the channels.     

Synthesis of Bis(2,4‐diarylimidazol‐5‐yl) Diselenides from N‐Benzylbenzimidoyl Isoselenocyanates

The reaction of N‐benzylbenzamides 6 with SOCl₂ under reflux gave the corresponding N‐benzylbenzimidoyl chlorides 7 . Further treatment with KSeCN in dry acetone yielded imidoyl isoselenocyanates 3 (Scheme 2). These compounds, obtained in satisfying yields, proved to be stable enough to be purified and analyzed. Reaction of 3 with morpholine in dry acetone led to the corresponding selenourea derivatives 8 . On treatment with Et₃N, the 4‐nitrobenzyl derivatives of type 3 were transformed into bis(2,4‐diarylimidazol‐5‐yl) diselenides 9 (Scheme 3). This transformation takes place only when the benzyl residue bears an NO₂ group and the phenyl group is not substituted with a strong electron‐donating group. A reaction mechanism for the formation of 9 is proposed in Scheme 4. The key structures have been established by X‐ray crystallography.     

Molecular complexes of dimethyl sulfoxide with tri‐ and dichloromethane

Crystals of molecular complexes of dimethyl sulfoxide with trichloromethane (chloroform), (CH₃)₂SO·2CHCl₃, (I), and dichloromethane, (CH₃)₂SO·CH₂Cl₂, (II), have been grown in situ. In both compounds, the components are linked together by (Cl)C—H...O interactions. The dimethyl sulfoxide molecules in (I) are bound into chains by C—H...O interactions. In (II), pairs of the components form centrosymmetric rings, linked into a three‐dimensional network by C—H...O contacts and dipole–dipole interactions between dimethyl sulfoxide molecules.     

An Expeditious Synthesis of Methyl Jasmonate

We present an efficient three‐step, two‐pot synthesis of methyl jasmonate (trans‐ 1 ) based on Diels–Alder cycloaddition of cyclopent‐2‐enone ( 2 ) and chloroprene (= 2‐chlorobuta‐1,3‐diene; 3d ) in either CHCl₃ or CH₂Cl₂, catalyzed by SnCl₄ (0.2 mol‐equiv.) at 20° (75% yield). Subsequent ozonolysis of a cis/trans 55 : 45 mixture of the cycloadduct 4d in either CH₂Cl₂ or AcOEt at ? 78°, followed by addition of Me₂S and MeOH in the presence of NaHCO₃, afforded, in 64% yield, a cis/trans 40 : 60 mixture of the known aldehyde 5c . The latter was reacted at ? 50° under salt‐free conditions with the propyl Wittig reactant to furnish 1 as a cis/trans 20 : 80 mixture ((E/Z) 3 : 97). Alternatively, a cis/trans 7 : 93 mixture ((E/Z) 4 : 96) was obtained in 88% yield from epimerized 5c (AcOH, H₂O, 40°; 99%) under usual Wittig conditions at ? 20°.     

Preparation and structures of a series of phosphorus‐free Nickel(II) diamine complexes and their applications in hydrogenation of acetophenone

To develop economical and phosphorus‐free catalysts for hydrogenation of ketones, three new complexes, [Ni(1R,2R‐dpen)₂(H₂O)Cl]₂Cl₂· 2Et₂O (1), [Ni(1R,2R‐dpen)(phen)(CH₃OH)₂]Cl₂·2CH₃OH (2) and [Ni(1,8‐dan)₂(DMF)Cl]₂Cl₂· 3H₂O (3), and three reported compounds, [Ni(opda)(phen)Cl₂]·CH₃OH (4), [Ni(opda)₂Cl₂] (5) and [Ni(1,2‐dach)₂]Cl₂ (6), were prepared and the structures of new compounds were determined by single crystal X‐ray diffraction analysis, in which 1R,2R‐dpen, phen, 1,8‐dan, opda and 1,2‐dach denote 1R,2R‐1,2‐diphenylethylenediamine, 1,10‐phenanthroline, 1,8‐diaminonaphthalene, o‐phenylenediamine and 1,2‐diaminocyclohexane, respectively. The catalytic effects for hydrogenation of acetophenone of these compounds were tested. This revealed very poor or no catalytic effects of these complexes in transfer hydrogenation of acetophenone using isopropanol or HCOOH? NEt₃ as hydrogen source. However, they presented much better catalytic effects in ionic hydrogenation of acetophenone using H₂ gas as hydrogen source with a dependence of the catalytic effects on the base used in the hydrogenation reactions. The complexes represent a kind of green hydrogenation catalyst, although the conversion in the hydrogenation reactions is not as high as expected. Copyright © 2010 John Wiley & Sons, Ltd.     

Thermal‐ and Light‐Induced Spin Crossover in a Guest‐Dependent Dinuclear Iron(II) System

We previously reported the dinuclear material [Fe^II₂(ddpp)₂(NCS)₄] ? 4 CH₂Cl₂ ( 1? 4 CH₂Cl₂; ddpp=2,5‐di(2′,2′′‐dipyridylamino)pyridine) and its partially desolvated analogue ( 1? CH₂Cl₂), which undergo two‐ and one‐step spin‐crossover (SCO) transitions, respectively. Here, we manipulate the type and degree of solvation in this system and find that either a one‐ or two‐step spin transition can be specifically targeted. The chloroform clathrate 1? 4 CHCl₃ undergoes a relatively abrupt one‐step SCO, in which the two equivalent Fe^II sites within the dinuclear molecule crossover simultaneously. Partial desolvation of 1? 4 CHCl₃ to form 1? 3 CHCl₃ and 1? CHCl₃ occurs through single‐crystal‐to‐single‐crystal processes (monoclinic C2/c to P2₁/n to P2₁/n) in which the two equivalent Fe^II sites become inequivalent sites within the dinuclear molecule of each phase. Both 1? 3 CHCl₃ and 1? CHCl₃ undergo one‐step spin transitions, with the former having a significantly higher SCO temperature than 1? 4 CHCl₃ and the latter, and each has a broader SCO transition than 1? 4 CHCl₃, attributable to the overlap of two SCO steps in each case. Further magnetic manipulation can be carried out on these materials through reversibly resolvating the partially desolvated material with chloroform to produce the original one‐step SCO, or with dichloromethane to produce a two‐step SCO reminiscent of that seen for 1? 4 CH₂Cl₂. Furthermore, we investigate the light‐induced excited spin state trapping (LIESST) effect on 1? 4 CH₂Cl₂ and 1? CH₂Cl₂ and observe partial LIESST activity for the former and no activity for the latter.     

Syntheses and structures of three macrocyclic supramolecular complexes and one ZnII‐containing coordination polymer generated from a semi‐rigid multidentate N‐containing ligand

Semirigid organic ligands can adopt different conformations to construct coordination polymers with more diverse structures when compared to those constructed from rigid ligands. A new asymmetric semirigid organic ligand, 4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine ( L ), has been prepared and used to synthesize three bimetallic macrocyclic complexes and one coordination polymer, namely, bis(μ‐4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine)bis[dichloridozinc(II)] dichloromethane disolvate, [Zn₂Cl₄(C₁₂H₁₀N₆)₂]·2CH₂Cl₂, ( I ), the analogous chloroform monosolvate, [Zn₂Cl₄(C₁₂H₁₀N₆)₂]·CHCl₃, ( II ), bis(μ‐4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine)bis[diiodidozinc(II)] dichloromethane disolvate, [Zn₂I₄(C₁₂H₁₀N₆)₂]·2CH₂Cl₂, ( III ), and catena‐poly[[[diiodidozinc(II)]‐μ‐4‐{2‐[(pyridin‐3‐yl)methyl]‐2H‐tetrazol‐5‐yl}pyridine] chloroform monosolvate], {[ZnI₂(C₁₂H₁₀N₆)]·CHCl₃}_n, ( IV ), by solution reaction with ZnX₂ (X = Cl and I) in a CH₂Cl₂/CH₃OH or CHCl₃/CH₃OH mixed solvent system at room temperature. Complex ( I ) is isomorphic with complex ( III ) and has a bimetallic ring possessing similar coordination environments for both of the Zn^II cations. Although complex ( II ) also contains a bimetallic ring, the two Zn^II cations have different coordination environments. Under the influence of the I^? anion and guest CHCl₃ molecule, complex ( IV ) displays a significantly different structure with respect to complexes ( I )–( III ). C—H…Cl and C—H…N hydrogen bonds, and π–π stacking or C—Cl…π interactions exist in complexes ( I )–( IV ), and these weak interactions play an important role in the three‐dimensional structures of ( I )–( IV ) in the solid state. In addition, the fluorescence properties of L and complexes ( I )–( IV ) were investigated.     

o‐Carborane‐Based Anthracene: A Variety of Emission Behaviors

An o‐carborane‐based anthracene was synthesized, and single crystals, with incorporated solvent molecules, were obtained from the CHCl₃, CH₂Cl₂, and C₆H₆ solutions. The anthracene ring in the crystal is highly distorted by the formation of a π‐stacked dimer between the anthracene units. The crystals exhibited a variety of emission behaviors such as aggregation‐induced emission (AIE), crystallization‐induced emission (CIE), aggregation‐caused quenching (ACQ), and multichromism.     

New ethylzinc reagents with remarkable properties in palladium-catalyzed zinc-ene reactions

Pd-Catalyzed Zn-ene allylic olefinations with the new ethylzinc reagents Et? Zn? OSO₂CF₃ ( 4 ) and Et? Zn? OC(O)CF(MeO)CF₃ ( 5 ) in CH₂Cl₂ showed an unexpected trans-selectivity in the ring closure to cyclopentane derivatives (see Scheme 2 and Table 1). This strong trans-selectivity is in contrast with the corresponding known Zn-ene reaction using Et₂Zn in Et₂O which shows a high cis-selectivity (Table 1). The probable radical origin of the observed trans-selectivity is discussed. The Zn-ene reaction products of the type R? Zn? OSO₂CF₃ could be derivatized by the known protonation, iodination, and cyanation yielding 8–10 (Scheme 4 and Table 2), these derivatizations could furthermore be extended by allylation and oxidation reaction (→ 13, 15 , and 16 ; see Scheme 5).     

Reactions of Nucleosides with 1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU). Syntheses of N(3)-Methylene-Bridged Bis-uridines and Secouridine-Dinucleoside Analogs

Diasteroisomeric secouridine derivatives, appropriately protected and activated, served as starting compounds in the reactions with 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in various solvents (CH₂Cl₂, MeCN, or dimethylformamide (DMF)). Reactions with DBU/CH₂Cl₂ gave N(3)-methylene-bridged bis-secouridines and bis-uridines (Scheme 3), while the reactions with DBU in non-alkylating solvents resulted in formation of secdinucleosides as the result of intermolecular ‘dimerizations’ (Scheme 2).     

Formation of 6,10‐Diphenyl‐Substituted Heptalene‐4,5‐dicarboxylates

It is shown that 4,8‐diphenylazulene ( 1 ) can be easily prepared from azulene by two consecutive phenylation reactions with PhLi, followed by dehydrogenation with chloranil. Similarly, a Me group can subsequently be introduced with MeLi at C(6) of 1 (Scheme 2). This methylation led not only to the expected main product, azulene 2 , but also to small amounts of product 3 , the structure of which has been determined by X‐ray crystal‐structure analysis (cf. Fig. 1). As expected, the latter product reacts with chloranil at 40° in Et₂O to give 2 in quantitative yields. Vilsmeier formylation of 1 and 2 led to the formation of the corresponding azulene‐1‐carbaldehydes 4 and 5 . Reduction of 4 and 5 with NaBH₄/BF₃ ? OEt₂ in diglyme/Et₂O 1 : 1 and BF₃ ? OEt₂, gave the 1‐methylazulenes 6 and 7 , respectively. In the same way was azulene 9 available from 6 via Vilsmeier formylation, followed by reduction of azulene‐1‐carbaldehyde 8 (Scheme 3). The thermal reactions of azulenes 1, 6 , and 7 with excess dimethyl acetylenedicarboxylate (ADM) in MeCN at 100° during 72 h afforded the corresponding heptalene‐4,5‐dicarboxylates 11, 12 , and 13 , respectively (Scheme 4). On the other hand, the highly substituted azulene 9 gave hardly any heptalene‐4,5‐dicarboxylate.     

Synthesis of 1,2,4‐Triazolo[4,3‐a]pyrimidine Derivatives by Cyclocondensation of a 2‐Thioxopyrimidin‐4(3H)‐one with Hydrazonoyl Halides

The reaction of 1,2‐dihydro‐6‐(phenylamino)‐2‐thioxopyrimidin‐4(3H)one ( 16 ) with N‐arylhydrazonoyl halides 15 in CHCl₃ in the presence of Et₃N under reflux afforded the corresponding 1,2,4‐triazolo[4,3‐a]pyrimidin‐5‐ones of type 20 in good yields (Scheme 3). The structure of one of the derivatives, 20d , has been established by X‐ray crystallography. Conceivable reaction mechanisms are discussed in Schemes 3 and 4. The products of type 20 easily undergo reactions with electrophiles such as benzenediazonium chloride, chloroacetyl chloride, and NaNO₂ in AcOH to give 6‐phenylazo, 6‐chloroacetyl, and 6‐nitroso derivatives 21, 23 , and 25 , respectively (Scheme 5).