Stable Mixed‐Valent Radicals from Platinum(II) Complexes of a Bis(dioxolene) Ligand

Three diplatinum(II) complexes [{PtL}₂(μ‐thea)] (H₄thea=2,3,6,7‐tetrahydroxy‐9,10‐dimethyl‐9,10‐dihydro‐9,10‐ethanoanthracene) have been prepared, with diphosphine or bipyridyl “L” co‐ligands. One‐electron oxidation of these complexes gave radical cations containing a mixed‐valent [thea]^3? ligand with discrete catecholate and semiquinonate centers separated by quaternary methylene spacers. The electronic character of these radicals is near the Robin–Day class II/III border determined by UV/Vis/NIR and EPR spectroscopies. Crystal‐structure determinations and a DFT calculation imply that oxidation of the thea^4? ligand may lead to an increased through‐space interaction between the dioxolene π systems.     

One‐Pot Syntheses of 2‐(2‐Sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic Acid Derivatives via Reactions of 3‐(2‐Isothiocyanatophenyl)prop‐2‐enoic Acid Derivatives with Thiols or Sodium Sulfide

Two efficient methods for the preparation of 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 3 under mild conditions have been developed. The first method is based on the reaction of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoates 1a – 1c with thiols in the presence of Et₃N in THF at room temperature, leading to the corresponding dithiocarbamate intermediates 2 , which underwent spontaneous cyclization at the same temperature by an attack of the S‐atom at the prop‐2‐enoyl moiety in a 1,4‐addition manner (Michael addition) to give 2‐(2‐sulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetates in one pot. The second method involves treatment of 3‐(2‐isothiocyanatophenyl)prop‐2‐enoic acid derivatives 1b – 1d with Na₂S leading to the formation of 2‐(2‐sodiosulfanyl‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid intermediates 5 by a similar addition/cyclization sequence, which are then allowed to react with alkyl or aryl halides to afford derivatives 3 . 2‐(2‐Thioxo‐4H‐3,1‐benzothiazin‐4‐yl)acetic acid derivatives 6 can be obtained by omitting the addition of halides.     

“Spontaneous” Ambient Temperature Dehydrocoupling of Aromatic Amine–Boranes

The dehydrocoupling/dehydrogenation behavior of primary arylamine–borane adducts ArNH₂ ? BH₃ ( 3 a – c ; Ar= a : Ph, b : p‐MeOC₆H₄, c : p‐CF₃C₆H₄) has been studied in detail both in solution at ambient temperature as well as in the solid state at ambient or elevated temperatures. The presence of a metal catalyst was found to be unnecessary for the release of H₂. From reactions of 3 a , b in concentrated solutions in THF at 22 °C over 24 h cyclotriborazanes (ArNH‐BH₂)₃ ( 7 a , b ) were isolated as THF adducts, 7 a , b? THF, or solvent‐free 7 a , which could not be obtained via heating of 3 a – c in the melt. The μ‐(anilino)diborane [H₂B(μ‐PhNH)(μ‐H)BH₂] ( 4 a ) was observed in the reaction of 3 a with BH₃?THF and was characterized in situ. The reaction of 3 a with PhNH₂ ( 2 a ) was found to provide a new, convenient method for the preparation of dianilinoborane (PhNH)₂BH ( 5 a ), which has potential generality. This observation, together with further studies of reactions of 4 a , 5 a , and 7 a , b , provided insight into the mechanism of the catalyst‐free ambient temperature dehydrocoupling of 3 a – c in solution. For example, the reaction of 4 a with 5 a yields 6 a and 7 a . It was found that borazines (ArN‐BH)₃ ( 6 a – c ) are not simply formed via dehydrogenation of cyclotriborazanes 7 a – c in solution. The transformation of 7 a to 6 a is slowly induced by 5 a and proceeds via regeneration of 3 a . The adducts 3 a – c also underwent rapid dehydrocoupling in the solid state at elevated temperatures and even very slowly at ambient temperature. From aniline–borane derivative 3 c , the linear iminoborane oligomer (p‐CF₃C₆H₄)N[BH‐NH(p‐CF₃C₆H₄)]₂ ( 11 ) was obtained. The single‐crystal X‐ray structures of 3 a – c , 5 a , 7 a , 7 b? THF, and 11 are discussed.     

Encapsulation with the Protrusion of Cruciform 9,10‐Bis(arylethynyl)anthracene Derivatives in a Self‐Assembled Boronic Ester Cavitand Capsule: Photochemical and Photophysical Properties

The self‐assembled boronic ester cavitand capsule 3 quantitatively and tightly encapsulates 2,6‐diacetoxy‐9,10‐bis(arylethynyl)anthracene derivatives 4 a – 4 c as highly fluorescent cruciform guests to form complexes 4 a @ 3 , 4 b @ 3 , and 4 c @( 3 )₂. The structural features of capsule 3 , which possesses two polar bowl‐shaped aromatic cavity ends and four large equatorial windows connected by dynamic boronic ester bonds, made it possible to encapsulate cruciform 4 with protection of the reactive anthracene core inside the capsule and with two protruding arylethynyl groups, the π‐conjugated arms of compound 4 , through two of the equatorial windows of the capsule. Thus, complexes 4 a @ 3 , 4 b @ 3 , and 4 c @( 3 )₂ show greater resistance to photochemical reactions in solution and fluorescence quenching in the powder state compared to free guests 4 . In addition to the improved photostability, restriction of the free rotation of the arylethynyl groups of guests 4 upon encapsulation results in sharpening of the UV/Vis absorption peaks with a red‐shift and a significant increase in some of the two‐photon‐absorption peaks of complexes 4 a @ 3 , 4 b @ 3 , and 4 c @( 3 )₂ compared with free guests 4 .     

A New Route to Vitamin E Key‐Intermediates by Olefin Cross‐Metathesis

Ru‐Catalyzed olefin cross‐metathesis (CM) has been successfully applied to the synthesis of several phytyl derivatives ( 2b, 2d – f, 3b ) with a trisubstituted C?C bond, as useful intermediates for an alternative route to α‐tocopheryl acetate (vitamin E acetate; 1b ) (Scheme 1). Using the second‐generation Grubbs catalyst RuCl₂(C₂₁H₂₆N₂)(CHPh)PCy₃ (Cy = cyclohexyl; 4a ) and Hoveyda–Grubbs catalyst RuCl₂(C₂₁H₂₆N₂){CH‐C₆H₄(O‐ⁱPr)‐2} ( 4b ), the reactions were performed with various C‐allyl ( 5a – f, 7a,b ) and O‐allyl ( 8a – d ) derivatives of trimethylhydroquinone‐1‐acetate as substrates. 2,6,10,14‐Tetramethylpentadec‐1‐ene ( 6a ) and derivatives 6c – e of phytol ( 6b ) as well as phytal ( 6f ) were employed as olefin partners for the CM reactions (Schemes 2 and 5). The vitamin E precursors could be prepared in up to 83% isolated yield as (E/Z)‐mixtures.     

Protecting‐Group‐Free Total Synthesis of Isoquinoline Alkaloids by Nickel‐Catalyzed Annulation of o‐Halobenzaldimine with an Alkyne as the Key Step

An efficient short total synthesis of benzo[c]phenanthridine alkaloids including oxyavicine, oxynitidine, and oxysanguinarine is described. Thus, N‐methyl‐o‐bromobenzaldimines 1 b – d undergo regioselective cyclization with 4‐(benzo[d][1,3]dioxol‐5‐yl)but‐3‐yn‐1‐ol ( 2 b ) in the presence of [Ni(cod)₂] (cod=1,5‐cyclooctadiene). In situ oxidation of the resultant isoquinolinium salts gives isoquinolinone derivatives 5 b – d with benzo[d][1,3]dioxol‐5‐yl substitution at the C₃ atom and a (CH₂)₂OH group at the C₄ atom. Later, oxidation of the alcohol group in 5 b – d to the aldehyde moiety followed by acid‐catalyzed cyclization and dehydration completes the total syntheses to give oxyavicine, oxynitidine, and oxysanguinarine in 67, 65, and 60 % yields, respectively. The synthesis requires four steps from o‐bromobenzaldehyde derivatives. Transformations of these alkaloids to the other alkaloids in this family are also discussed herein.     

Dendron‐Containing Tetraphenylethylene Compounds: Dependence of Fluorescence and Photocyclization Reactivity on the Dendron Generation

The synthesis and characterization of four dendron‐containing tetraphenylethylenes (TPEs), 1₁ – 1₄ , were synthesized, along with a TPE compound that contained four OCH₂Ph groups (referred to as 1₀ ) for comparison. Photophysical studies revealed that the TPE core became emissive after linking dendrons onto its periphery. Moreover, the fluorescence intensity was significantly enhanced when high‐generation dendrons were linked onto the TPE core; the fluorescence intensity increased in the following order: 1₁ < 1₂ < 1₃ < 1₄ . This phenomenon was tentatively attributed to an enhancement in the energy barrier for internal rotation and torsion of the TPE core to which four dendrons were connected. In addition, the photocyclization of the TPE core into the respective 9,10‐diphenylphenanthrene was facilitated when high‐generation dendrons were linked to the TPE core. Again, the photocycliztion reactivity increased in the following order: 1₁ < 1₂ < 1₃ < 1₄ . We found that the fluorescence and photocyclization reactivity of TPE could be modulated by covalent interactions with dendrons, and such modulation was strongly dependent on the dendron‐generation.     

Radical Cyclization Reactions via Manganese(III) Acetate Leading to 2‐Thienyl‐Substituted Dihydrofuran Compounds

The 2‐thienyl‐substituted 4,5‐dihydrofuran derivatives 3 – 8 were obtained by the radical cyclization reaction of 1,3‐dicarbonyl compounds 1a – 1f with 2‐thienyl‐substituted conjugated alkenes 2a – 2e by using [Mn(OAc)₃] (Tables 1–5). In this study, reactions of 1,3‐dicarbonyl compounds 1a – 1e with alkenes 2a – 2c gave 4,5‐dihydrofuran derivatives 3 – 5 in high yields (Tables 1–3). Also the cyclic alkenes 2d and 2e gave the dihydrobenzofuran compounds, i.e., 6 and 7 in good yields (Table 4). Interestingly, the reaction of benzoylacetone (=1‐phenylbutane‐1,3‐dione; 1f ) with some alkenes gave two products due to generation of two stable carbocation intermediates (Table 5).     

An Efficient Synthesis of Novel Benzo‐Fused Macrocyclic Dilactams

A facile synthetic approach was adopted towards the synthesis of benzo‐fused macrocyclic lactams 2a – 2g via the base‐catalyzed condensation reaction of 2,2′‐[alkanediylbis(oxy)]bis[benzaldehydes] 3a – 3c with N,N′‐substituted bis[2‐cyanoacetamide] derivatives 7a – 7c (Scheme 2). The latter compounds were obtained by the reaction of the appropriate diamines 6a – 6c with ethyl 2‐cyanoacetate ( 4 ). Attempts to prepare the oxaaza macrocycles 2 by alternative pathways were also investigated. The novel pyrazolo‐fused macrocycles 13a and 13b were obtained in 48 and 52% yield, respectively, upon treatment of 2d and 2g with NH₂NH₂?H₂O at 100° (Scheme 4).     

Synthesis,Characterization, and Electrochemistry of the Manganese(I) Complexes of meso‐Substituted [14]Tribenzotriphyrins(2.1.1)

Metalation of 6,13,20,21‐tetraaryl‐22H‐[14]tribenzotriphyrins(2.1.1) (TriP, 1 a – d ) with [Mn(CO)₅Br] provided Mn^I tricarbonyl complexes of [14]tribenzotriphyrins(2.1.1) 2 a – d in 85–93 % yield. The complexes were characterized by mass spectrometry and UV/Vis absorption, IR, and NMR spectroscopy. Single‐crystal X‐ray analyses revealed that 2 b and 2 c adopt bowl‐shaped conformations. The redox properties of [(TriP)Mn^I(CO)₃] ( 2 a – d ) were studied by cyclic voltammetry. Each compound undergoes two reversible one‐electron reductions to form a porphyrin π anion radical and a dianion in CH₂Cl₂. Two oxidation waves were observed, the first of which corresponds to a metal‐centered electron‐transfer process. The redox potentials of 2 a – d are consistent with the optical spectroscopic data and the relatively narrow HOMO–LUMO gaps that were predicted in DFT calculations. The optical spectra can be assigned by using Michl’s perimeter model. TDDFT calculations predict the presence of several metal‐to‐ligand charge‐transfer bands in the L‐band region between 500 and 700 nm.     

The electrochemistry of some ferrocene derivatives: redox potential and substituent effects

Fifteen ferrocene derivatives I–IX (four of which have been prepared for the first time: II, IIIf, V and VIII) have been prepared by Friedel–Crafts acetylation, Claisen condensation, Michael reaction, and ring closure by hydrazine hydrate. The anodic behaviour of these compounds has been studied by cyclic voltammetry at a platinum electrode in an aprotic solvent. All these substituted ferrocenes exhibit a reversible one‐electron oxidation reduction centred at each iron centre, and the effect of substituents on the half‐wave oxidation potential is discussed in terms of their electronic properties. Linear correlations have been observed between these potentials and the Hammett σ_x constant for the substituents. Cyclic voltammetry has been carried out for ferrocene derivatives IIIa, V and IX. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis of Biologically Active[4-(4-Bromophenyl)-2-thiazolyl]hydrazones and their D-Galactose Derivatives

Benzaldehyde [4‐(4‐bromophenyl)thiazol‐2‐yl]hydrazones 5a – 5d were prepared by reacting the thiosemicarbazones 2a – 2d with 2,4′‐dibromoacetophenone ( 1 ) in absolute ethanol. Acetylation of 5a and 5b with Ac₂O/Py at room temperature gave the N‐acetyl derivatives 6a and 6b . 4‐Methyl‐2‐pentanone/cyclopentanone [4‐(4‐bromo‐phenyl)thiazol‐2‐yl]hydrazones ( 8a ) and ( 8b ) were similarly obtained from the reaction of 1 with the thiosemicarbazones 7a and 7b , respectively. Cyclization of D‐galactose thiosemicarbazone ( 9 ) and its tautomers 10 and 11 with 1 afforded an equilibrium mixture of the acyclic 2‐thiazolylhydrazone 12 , together with its respective cyclic galactosyl derivatives 13 and 14 , whose structures were studied by using ¹H and ¹³C NMR spectra. The antimicrobial activity of the synthesized thiazole derivatives was evaluated in vitro by using an agar diffusion technique, and some of these compounds showed potential activity against Candida albicans.     

Vaulted trans‐Bis(salicylaldiminato)platinum(II) Crystals: Heat‐Resistant,Chromatically Sensitive Platforms for Solid‐State Phosphorescence at Ambient Temperature

The synthesis, structure, and solid‐state emission of vaulted trans‐bis(salicylaldiminato)platinum(II) complexes are described. A series of polymethylene ( 1 : n=8; 2 : n=9; 3 : n=10; 4 : n=11; 5 : n=12; 6 : n=13) and polyoxyethylene ( 7 : m=2; 8 : m=3; 9 : m=4) vaulted complexes (R=H ( a ), 3‐MeO ( b ), 4‐MeO ( c ), 5‐MeO ( d ), 6‐MeO ( e ), 4‐CF₃O ( f ), 5‐CF₃O ( g )) was prepared by treating [PtCl₂(CH₃CN)₂] with the corresponding N,N′‐bis(salicylidene)‐1,ω‐alkanediamines. The trans coordination, vaulted structures, and the crystal packing of 1 – 9 have been unequivocally established from X‐ray diffraction studies. Unpredictable, structure‐dependent phosphorescent emission has been observed for crystals of the complexes under UV excitation at ambient temperature, whereas these complexes are entirely nonemissive in the solution state under the same conditions. The long‐linked complex crystals 4 – 6 , 8 , and 9 exhibit intense emission (Φ_77K=0.22–0.88) at 77 K, whereas short‐linked complexes 1 – 3 and 7 are non‐ or slightly emissive at the same temperature (Φ_77K<0.01–0.18). At 298 K, some of the long‐linked crystals, 4 a , 4 b , 5 c , 5 e , 6 c , 6 e , and 9 b , completely lose their high‐emission properties with elevation of the temperature (Φ_298K<0.01–0.02), whereas the other long‐linked crystals, 5 a , 6 a , 9 a , and 9 d , exhibit high heat resistance towards emission decay with increasing temperature (Φ_298K=0.21–0.38). Chromogenic control of solid‐state emission over the range of 98 nm can be performed simply by introducing MeO groups at different positions on the aromatic rings. Orange, yellow‐green, red, and yellow emissions are observed in the glass and crystalline state upon 3‐, 4‐, 5‐, and 6‐MeO substitution, respectively, whereas those with CF₃O substituents have orange emission, irrespective of the substitution position. DFT calculations (B3LYP/6‐31G*, LanL2DZ) showed that such chromatic variation is ascribed to the position‐specific influence of the substituents on the highest‐occupied molecular orbital (HOMO) and lowest‐unoccupied molecular orbital (LUMO) levels of the trans‐bis(salicylaldiminato)platinum(II) platform. The solid‐state emission and its heat resistance have been discussed on the basis of X‐ray diffraction studies. The planarity of the trans‐coordination sites is strongly correlated to the solid‐state emission intensities of crystals 1 – 9 at lower temperatures. The specific heat‐resistance properties shown exclusively by the 5 a , 6 a , 9 a , and 9 d crystals are due to their strong three‐dimensional hydrogen‐bonding interactions and/or Pt???Pt contacts, whereas heat‐quenchable crystals 4 a , 4 b , 5 c , 5 e , 6 c , 6 e , and 9 b are poorly bound with limited interactions, such as non‐, one‐, or two‐dimensional hydrogen‐bonding networks. These results lead to the conclusion that Pt???Pt contacts are an important factor in the heat resistance of solid‐state phosphorescence at ambient temperature, although the role of Pt???Pt contacts can be substituted by only higher‐ordered hydrogen‐bonding fixation.     

New Bifunctional Benzoxazaphosphorinanone Systems

The (CH₂)_n (n = 2, 3)‐bridged, PCl‐functional bis(benzoxazaphosphorinanone) derivatives, 3 a and 3 b , were prepared in high yield by the reaction of the salicylic acid amide derivatives, 2 a and 2 b , with phosphorus trichloride. Cyclocondensation of 3 a and 3 b with the bis(trimethylsilyl)ethers, 4 a – 4 c , furnished the symmetrical benzoxazaphosphorinanone derivatives, 5 a – 5 f , in moderate yield. 5 a – 5 f involve a nine‐membered ring, made up of carbon, nitrogen, phosphorus, and oxygen, as a central feature. Oxidation of  5 a – 5 f with the urea‐hydrogen peroxide adduct, (H₂N)₂C(:O) · H₂O₂, gave rise to the corresponding phosphoryl compounds, 6 a – 6 f . All new compounds were characterized by NMR spectroscopy, mass spectrometry, and elemental analysis. For compound 6 e an X‐ray crystal structure determination was conducted; the two formally identical halves of the molecule differ appreciably in the torsion angles in the region P–O–C (naphthyl).     

Preparations of Saturated N‐P‐N Type Secondary Phosphine Oxides and their Applications in Cross‐Coupling Reactions

A series of cyclohexane‐1,2‐diamine ( 3a – 3d ) and benzene‐1,2‐diamine derivatives ( 3e – 3h ) were pre‐ pared. Followed by hydrolysis, the reaction of 3a – 3c with PCl₃ successfully led to the formation of cor‐ responding metastable saturated heteroatom‐substituted secondary phosphine oxides (HASPO 4a – 4c ), a tautomer of the saturated heteroatom‐substituted phosphinous acid (HAPA). Whereas ambient‐stable diamine‐coordinated palladium complexes were obtained, HAPA‐coordinated palladium complexes were not successfully synthesized. The molecular structures of HASPO 4c , Pd(OAc)₂(3a) , PdBr₂(3b) and Pd(OAc)₂(3c) and [Cu(NO₃)(3d)⁺][NO₃ ^? ] were determined by single‐crystal X‐ray diffraction method. Catalysis of in‐situ Suzuki‐Miyaura cross‐coupling reactions for aryl bromides and phenylboronic acid using diamine 3a as ancillary ligand showed that the optimized reaction condition at 60 °C is the combination of 2 mmol % 3a /3.0 mmol KOH/1.0 mL 1,4‐dioxane/1 mmol % Pd(OAc)₂. Moreover, moderate reactivity was observed when using aryl chlorides as substrates (supporting infor‐ mation). When diamine 3d was employed in Heck reaction, good tolerance of functional groups of aryl bromides were observed while using 4‐bromoanisole and styrene as substrates. The optimized condi‐ tion for Heck reaction at 100 °C is 3 mmol % 3d /3.0 mmol CsF/1.0 mL toluene/3 mmol % Pd(OAc)₂. In general, cyclohexane‐1,2‐diamine derivatives exhibited better catalytic properties than those of benzene‐1,2‐diamines.     

Regio‐ and Stereoselective Reductive Coupling of Bicyclic Alkenes with Propiolates Catalyzed by Nickel Complexes: A Novel Route to Functionalized 1,2‐Dihydroarenes and γ‐Lactones

7‐Oxabenzonorbornadienes derivatives 1 a – d underwent reductive coupling with alkyl propiolates CH₃C?CCO₂CH₃ ( 2 a ), PhC?CCO₂Et ( 2 b ), CH₃(CH₂)₃C?CCO₂CH₃ ( 2 c ), CH₃(CH₂)₄C?CCO₂CH₃ ( 2 d ), TMSC?CCO₂Et ( 2 e ), (CH₃)₃C?CCO₂CH₃ ( 2 f ) and HC?CCO₂Et ( 2 g ) in the presence of [NiBr₂(dppe)] (dppe=Ph₂PCH₂CH₂PPh₂), H₂O and zinc powder in acetonitrile at room temperature to afford the corresponding 2alkenyl‐1,2‐dihydronapthalen‐1‐ol derivatives 3 a – n with remarkable regio‐ and diastereoselectivity in good to excellent yields. Similarly, the reaction of 7azabenzonorbornadienes derivative 1 e with propiolates 2 a, b and d proceeded smoothly to afford reductive coupling products 2alkenyl‐1,2‐dihydronapthalene carbamates 3 o – p in good yields with high regio‐ and stereoselectivity. This nickel‐catalyzed reductive coupling can be further extended to the reaction of 7oxabenzonorbornene derivatives. Thus, 5,6‐di(methoxymethyl)‐7‐oxabicyclo[2.2.1]hept‐2‐ene ( 4 ) reacted with 2 a and 2 d to furnish cyclohexenol derivatives bearing four cis substituents 5 a and b in 81 and 84 % yield, respectively. In contrast to the results of 4 with 2 , the reaction of dimethyl 7oxabicyclo[2.2.1]hept‐5‐ene‐2,3‐dicarboxylate ( 6 ) with propiolates 2 a – d afforded the corresponding reductive coupling/cyclization products, bicyclo[3.2.1]γ‐lactones 7 a – d in good yields. The reaction provides a convenient one‐pot synthesis of γ‐lactones with remarkably high regio‐ and stereoselectivity.     

Solvatochromism,Reversible Chromism and Self‐Assembly Effects of Heteroatom‐Assisted Aggregation‐Induced Enhanced Emission (AIEE) Compounds

Two compounds, 9,10‐bis[2‐(quinolyl)vinyl]anthracene (BQVA) and 9,10‐bis[2‐(naphthalen‐2‐yl)vinyl]anthracene (BNVA), have been synthesised and investigated. Both of them have aggregation‐induced enhanced emission (AIEE) properties. Heteroatom‐assisted BQVA shows solvatochromism, reversible chromism properties and self‐assembly effects. When increasing the solvent polarities, the green solution of BQVA turns to orange with a redshift of the fluorescence emission wavelengths from λ=527 to 565 nm. Notably, BQVA exhibits reversible chromism properties, including mechano‐ and thermochromism. The as‐prepared BQVA powders show green fluorescence (λ_em=525 nm) and the colour can turn into orange (λ_em=573 nm) after grinding. Interestingly, the orange colour can return at high temperature. Based on these reversible chromism properties, a simple and convenient erasable board has been designed. Different from BQVA, non‐heteroatom‐assisted BNVA has no clear chromic processes. The results obtained from XRD, differential scanning calorimetry, single‐crystal analysis and theoretical calculations indicate that the chromic processes depend on the heteroatoms in BQVA. Additionally, BQVA also exhibits excellent self‐assembly effects in different solvents. Homogeneous nanospheres are formed in mixtures of tetrahydrofuran and water, which are then doped into silica nanoparticles and treated with 3‐aminopropyltriethoxysilane to give amino‐functionalised nanoparticles (BQVA?AFNPs). The BQVA?AFNPs could be used to stain protein markers in polyacrylamide gel electrophoresis.     

Chemoselectivity of the Reactions of Diazomethanes with 5‐Benzylidene‐3‐phenylrhodanine

The reactions of 5‐benzylidene‐3‐phenylrhodanine ( 2 ; rhodanine=2‐thioxo‐1,3‐thiazolidin‐4‐one) with diazomethane ( 7a ) and phenyldiazomethane ( 7b ) occurred chemoselectively at the exocyclic C?C bond to give the spirocyclopropane derivatives 9 and, in the case of 7a , also the C‐methylated products 8 (Scheme 1). In contrast, diphenyldiazomethane ( 7c ) reacted exclusively with the C?S group leading to the 2‐(diphenylmethylidene)‐1,3‐thiazolidine 11 via [2+3] cycloaddition and a ‘two‐fold extrusion reaction’. Treatment of 8 or 9b with an excess of 7a in refluxing CH₂Cl₂ and in THF at room temperature in the presence of [Rh₂(OAc)₄], respectively, led to the 1,3‐thiazolidine‐2,4‐diones 15 and 20 , respectively, i.e., the products of the hydrolysis of the intermediate thiocarbonyl ylide. On the other hand, the reactions with 7b and 7c in boiling toluene yielded the corresponding 2‐methylidene derivatives 16, 21a , and 21b . Finally, the reaction of 11 with 7a occurred exclusively at the electron‐poor C?C bond, which is conjugated with the C?O group. In addition to the spirocyclopropane 23 , the C‐methylated 22 was formed as a minor product. The structures of the products (Z)‐ 8, 9a, 9b, 11 , and 23 were established by X‐ray crystallography.     

Realization of Rhodium Metal‐Oxide Electrode in Indifferent Electrolytes

The pH‐dependence of the stationary open‐circuit potential E_i=0^st of rhodium electrode with a surface layer of anodically formed insoluble compounds has been studied in sulfate and phosphate solutions by means of cyclic voltammetry and chronopotentiometry. The range of potentials of the investigations performed has been confined to the region of rhodium electrochemical oxidation/reduction, i.e., 0.2<E<1.2 V (RHE) in order to prevent any possible interference of other reactions such as H₂ and O₂ evolution. It has been shown that rhodium electrode with a layer of surface compounds formed anodically at E<<1.23 V (RHE) behaves like a reversible metal‐oxide electrode within the range of pH values from ca. 1.0 to ca. 8.0. It has been presumed that the stationary potential of such electrode is determined by the equilibrium of the following electrochemical reaction: Rh+3H₂O??Rh(OH)₃+3H⁺+3e^?. The pH‐dependence of the reversible potential of Eequation/tex2gif-inf-6.gif electrode has been found to be: Eequation/tex2gif-inf-8.gif=E_i=0^st=0.69?0.059 pH, V. In acid solutions (pH<2.0) rhodium hydroxide dissolves into the electrolyte, therefore, to reach equilibrium, the solution must be saturated with Rh(OH)₃. This has been achieved by adding Rh³⁺ ions in the form of Rh₂(SO₄)₃. The solubility product of Rh(OH)₃, estimated from the experimental Eequation/tex2gif-inf-16.gif?pH dependence obtained, is ca. 1.0×10^?48, which is close to the value given in literature.     

Synthesis of Dihydropyrans and Dihydrofurans via Radical Cyclization of Unsaturated Alcohols and 1,3‐Dicarbonyl Compounds

The oxidative cyclization reactions of 1,3‐dicarbonyl compounds 1a – 1c and α,β‐unsaturated alcohols 2a – 2f with Mn(OAc)₃ were performed, leading to dihydrofurans. Treatment of 1a and 1b with 2‐methylbut‐3‐en‐2‐ol ( 2a ) gave dihydrofurans 3aa and 3ba , and dihydropyrans 4aa and 4ba , as unexpected products. While the reaction of 2‐methylbut‐3‐yn‐2‐ol ( 2b ) with acetylacetone ( 1b ) yielded a bifuran, ethyl acetoacetate ( 1a ) led to a mixture of furan, bifuran, and salicylate derivatives. Besides, surprisingly, styryl‐substituted dihydrofurans were obtained from the reactions of 1,3‐dicarbonyl compounds and (3E)‐2,4‐diphenylbut‐3‐en‐2‐ol. The reaction mechanisms were proposed for the formation of the different products, considering intermediates in these reaction mixtures.