Synthesis of 1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene: A Reactive s‐cis‐Butadiene Undergoing Highly Chemo‐ and Regioselective Cyclodimerization

1,2,3,4‐Tetrahydro‐1,2‐dimethylidenenaphthalene 11 has been derived in three steps from tetralone. In the condensed state and at −80°, it undergoes a highly chemo‐ and regioselective cyclodimerization to give 3,3′,4,4′‐tetrahydro‐2‐methylidenespiro[naphthalene‐1(2H),2′(1′H)‐phenanthrene] ( 14 ), the structure of which has been established by single‐crystal X‐ray‐diffraction analysis. Dimer 14 undergoes cycloreversion to diene 11 under flash‐pyrolysis conditions. The reaction of diene 11 with SO₂ occurs without acid promoter at −80° and gives a mixture of (±)‐1,4,5,6‐tetrahydronaphth[1,2‐d][1,2]oxathiin 2‐oxide ( 23 ; a single sultine), 1,3,4,5‐tetrahydronaphtho[1,2‐c]thiophene 2,2‐dioxide ( 25 ), and dimer 14 . The high reactivity of diene 1 in its Diels‐Alder cyclodimerization and its highly regioselective hetero‐Diels‐Alder addition with SO₂ can be interpreted in terms of the formation of relatively stable diradical intermediates or by concerted processes with transition states that can be represented as diradicaloids.     

Substituent Effect on the Competition between Hetero‐Diels‐Alder and Cheletropic Additions of Sulfur Dioxide to 1‐Substituted Buta‐1,3‐dienes

The reactivity of sulfur dioxide toward variously substituted butadienes was explored in an effort to define the factors affecting the competition between the hetero‐Diels‐Alder and cheletropic additions. At low temperature (<−70°), 1‐alkyl‐substituted 1,3‐dienes 1 that can adopt s‐cis‐conformations add to SO₂ in the hetero‐Diels‐Alder mode in the presence of CF₃COOH as promoter. In the case of (E)‐1‐ethylidene‐2‐methylidenecyclohexane ((E)‐ 4a ), the [4+2] cycloaddition of SO₂ is fast at −90° without acid catalyst. (E)‐1‐(Acyloxy)buta‐1,3‐dienes (E)‐ 1c , (E)‐ 1y , and (E)‐ 1z with AcO, BzO, and naphthalene‐2‐(carbonyloxy) substituents, respectively also undergo the hetero‐Diels‐Alder addition with SO₂+CF₃COOH at low temperatures, giving a 1 : 10 mixture of the corresponding cis‐ and trans‐6‐(acyloxy)sultines c‐ 2c,y,z and t‐ 2c,y,z , respectively). Above −50°, the sultines undergo complete cycloreversion to the corresponding dienes and SO₂, which that add in the cheletropic mode at higher temperature to give the corresponding 2‐substituted sulfolenes (=2,5‐dihydrothiophene 1,1‐dioxides) 3 . The hetero‐Diels‐Alder additions of SO₂ follow the Alder endo rule, giving first the 6‐substituted cis‐sultines that equilibrate then with the more stable trans‐isomers. This statement is based on the assumption that the S=O group in the sultine prefers a pseudo‐axial rather than a pseudo‐equatorial position, as predicted by quantum calculations. The most striking observation is that electron‐rich dienes such as 1‐cyclopropyl‐, 1‐phenyl‐, 1‐(4‐methoxyphenyl)‐, 1‐(trimethylsilyl)‐, 1‐phenoxy‐, 1‐(4‐chlorophenoxy)‐, 1‐(4‐methoxyphenoxy)‐, 1‐(4‐nitrophenoxy)‐, 1‐(naphthalen‐2‐yloxy)‐, 1‐(methylthio)‐, 1‐(phenylthio)‐, 1‐[(4‐chlorophenyl)thio]‐, 1‐[(4‐methoxyphenyl)thio]‐, 1‐[(4‐nitrophenyl)thio]‐, and 1‐(phenylseleno)buta‐1,3‐diene, as well as 1‐(methoxymethylidene)‐2‐methylidenecyclohexane ( 4f ) do not equilibrate with the corresponding sultines between −100 and −10°, in the presence of a large excess of SO₂, with or without acidic promoter. The hetero‐Diels‐Alder additions of SO₂ to 1‐substituted (E)‐buta‐1,3‐dienes are highly regioselective, giving exclusively the corresponding 6‐substituted sultines. The 1‐substituted (Z)‐buta‐1,3‐dienes do not undergo the hetero‐Diels‐Alder additions with sulfur dioxide.     

Competition between Hetero‐Diels‐Alder and Cheletropic Additions of Sulfur Dioxide to 2‐Substituted Buta‐1,3‐dienes. Synthesis of 2‐(1‐Naphthyl)‐ and 2‐(2‐Naphthyl)buta‐1,3‐diene

Chloroprene (=2‐chlorobuta‐1,3‐diene; 4b ) and electron‐rich dienes such as 2‐methoxy‐( 4c ), 2‐acetoxy‐( 4d ), and 2‐(phenylseleno)buta‐1,3‐diene ( 4e ) refused to equilibrate with the corresponding sultines 5 or 6 between −80 and −10° in the presence of excess SO₂ and an acidic promoter. Isoprene ( 4a ) and 2‐(triethylsilyl)‐( 4f ), 2‐phenyl‐( 4g ), and 2‐(2‐naphthyl)buta‐1,3‐diene ( 4i ) underwent the hetero‐Diels‐Alder additions with SO₂ at low temperature. In contrast, 2‐(1‐naphthyl)buta‐1,2‐diene ( 4h ) did not. With dienes 4a, 4g , and 4i , the hetero‐Diels‐Alder additions with SO₂ gave the corresponding 4‐substituted sultine 5 with high regioselectivity. In the case of 4g +SO₂⇄ 5g , the energy barrier for isomerization of 5g to 5‐phenylsultine ( 6g ) was similar to that of the cheletropic addition of 4g to give 3‐phenylsulfolene ( 7g ). The hetero‐Diels‐Alder addition of 4f gave a 1 : 4 mixture of the 4‐(triethylsilyl)sultine ( 5f ) and 5‐(triethylsilyl)sultine ( 6f ). The preparation of the two new dienes 4h and 4i is reported.     

Computational Studies on Intramolecular Cycloadditions of Azidoenynes and Azidobutenenitriles to Give 6H‐Pyrrolo[1,2‐c][1,2,3]triazoles and 5H‐Pyrrolo[1,2‐d]tetrazoles

Energetics of intramolecular cycloadditions of azidoenynes and azidobutenenitriles to give 6H‐pyrrolo[1,2‐c][1,2,3]triazoles and 5H‐pyrrolo[1,2‐d]tetrazoles have been calculated at the B3LYP/6.311++G(3df,3pd) level of theory in ideal gas and in H₂O as solvent. Stabilities of the corresponding anions, tautomers, and isomers are discussed. Transition states of the cyclization of parent compounds are determined at the same level of theory.     

Reaction of sulfenes with heterocyclic N,N-disubstituted α-aminomethyleneketones. XII. Synthesis of [1]benzothiepino[4,5-e][1,2]oxathiin derivatives

The 1,4-cycloaddition of sulfene to N,N-disubstituted (E)-4-aminomethylene-3,4-dihydro[1]benzothiepin-5(2H)-ones I occurred only in the case of aliphatic N,N-disubstitution to give in good yield 4-dialkylamino-3,4,5,6-tetrahydro[1]benzothiepino[4,5-e][1,2]oxathiin 2,2-dioxides, which are derivatives of the new heterocyclic system [1]benzothiepino[4,5-e][1,2]oxathiin. Also the reaction of I with chlorosulfene occurred only in the case of aliphatic N,N-disubstitution to afford chiefly trans-4-dialkylamino-3-chloro-3,4,5,6-tetrahydro-[1]benzothiepino[4,5-e][1,2]oxathiin 2,2-dioxides III in satisfactory yield. Adducts III were dehydrochlorinated with DBN to 4-dialkylamino-5,6-dihydro[1]benzothiepino[4,5-e][1,2]oxathiin 2,2-dioxides in good yield.     

Synthesis,Structure, and Conformation of 2′,3′‐Fused Oxathiane and Thiomorpholine Uridines

The syntheses of two 2′,3′‐fused bicyclic nucleoside analogues, i.e., 1‐[(4aR,5R,7R,7aS)‐hexahydro‐5‐(hydroxymethyl)‐4,4‐dioxidofuro[3,4‐b][1,4]oxathiin‐7‐yl]pyrimidine‐2,4(1H,3H)‐dione ( 1a ) and 1‐[(4aS,5R,7R,7aS)‐hexahydro‐7‐(hydroxymethyl)‐1,1‐dioxido‐2H‐furo[3,4‐b][1,4]thiazin‐5‐yl]pyrimidine‐ 2,4(1H,3H)‐dione ( 1b ), are described, the key step being an intramolecular hetero‐Michael addition. Their structures and conformations, previously solved by X‐ray crystallography, were analyzed in more detail, using 1D‐ and 2D‐NMR as well as HR‐MS analyses.     

Interaction of 4‐Oxo‐4H‐pyrazolo[5,1‐c][1,2,4]triazin‐1‐ides with Grignard Reagents

Reactions of magnesium 3‐tert‐butyl‐8‐R‐4‐oxo‐4H‐pyrazolo[5,1‐c][1,2,4]triazin‐1‐ides (R = CN, CO₂Et) with AlkMgBr led to nucleophilic additions to either side chain or triazine core, with selectivity being dependent on the nature of substituents, as well as on the solvents used. Previously inaccessible C⁸‐functionalized and C⁴‐functionalized pyrazolo[5,1‐c][1,2,4]triazines and 3‐tert‐butyl‐3‐ethyl‐4‐oxo‐1,2,3,4‐tetrahydropyrazolo[5,1‐c][1,2,4]triazine were synthesized, and their reactivity and spectral data discussed.     

An Efficient Synthesis of Spiro‐oxindole Derivatives by Three‐Component Reactions in Water

An efficient synthesis of (3S)‐1,1′,2,2′,3′,4′,6′,7′‐octahydro‐9′‐nitro‐2,6′‐dioxospiro[3H‐indole‐3,8′‐[8H]pyrido[1,2‐a]pyrimidine]‐7′‐carbonitrile is achieved via a three‐component reaction of isatin, ethyl cyanoacetate, and 1,2,3,4,5,6‐hexahydro‐2‐(nitromethylidene)pyrimidine. The present method does not involve any hazardous organic solvents or catalysts. Also the synthesis of ethyl 6′‐amino‐1,1′,2,2′,3′,4′‐hexahydro‐9′‐nitro‐2‐oxospiro[3H‐indole‐3,8′‐[8H]pyrido[1,2‐a]pyrimidine]‐7′‐carboxylates in high yields, at reflux, using a catalytic amount of piperidine, is described. The structures were confirmed spectroscopically (IR, ¹H‐ and ¹³C‐NMR, and EI‐MS data) and by elemental analyses. A plausible mechanism for this reaction is proposed (Scheme 2).     

A Radical Tricationic Rhomboid Tetraborane(4) with Four‐Center,Five‐Electron Bonding

The red‐colored tetraborane(4) [B₄(hpp)₄]^3+. ( 3 ; hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a]pyrimidinate) with a rhomboid B₄ skeleton stabilized by four N donors, was synthesized by the reaction of the strong hydride abstraction reagent [(acridine)BCl₂][AlCl₄] with the electron‐rich diborane(4) [HB(hpp)]₂ ( 1 ). The salt 3 [AlCl₄]₃ was structurally characterized and the presence of unpaired electrons proven by EPR measurements. The unprecedented radical tricationic 3 is distinguished by a high positive charge and boron atoms in a low oxidation state (less than two).     

Synthesis of anionic hypervalent cyclic selenenate esters: relevance to the hypervalent intermediates in nucleophilic substitution reactions at the selenium(II) center

The synthesis of a diaryl diselenide that contains 2,6‐dicarboxylic acid groups, 2,2′‐diselanediylbis(5‐tert‐butylisophthalic acid) ( 10 ), is described. Diselenide 10 undergoes intramolecular cyclization in methanol to form a cyclic selenenate ester, 5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylic acid ( 11 ). The cyclization reaction proceeds more rapidly in the presence of organic bases, such as pyridine, adenine, and 4,4′‐bipyridine, to form pyridinium 5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylate ( 14 ), adeninium 5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylate ( 15 ), and 4,4′‐bipyridiniumbis(5‐tert‐butyl‐3‐oxo‐3H‐benzo[c][1,2]oxaselenole‐7‐carboxylate) ( 16 ), respectively. However, 2,2′‐diselanediyldibenzoic acid ( 22 ) does not undergo cyclization under similar conditions. Structural studies on cyclic selenenate esters 14 – 16 revealed that the Se???O (COO^?) secondary distances (2.170, 2.075, and 2.176 Å) were significantly shorter than the corresponding Se???O distances (2.465, 2.472, and 2.435 Å) observed for the selenenate esters stabilized by the neutral donors (CHO, COOH, and COOEt). ¹H, ¹³C, and ⁷⁷Se NMR spectroscopy of compounds 11 and 14 – 16 reveal that the aryl protons of compound 11 and the organic cations of compounds 14 – 16 exchange between the two carboxylate groups via a hypercoordinate intermediate. The corresponding hypercoordinate intermediate ( 14 b , pyridinium selenuranide) for compound 14 was detected at low temperatures using ⁷⁷Se NMR spectroscopy. The presumed hypercoordinate intermediates in the carboxylate‐exchange reactions at the selenium(II) center for a set of model reactions were optimized using DFT‐B3LYP/6–311+g(d) calculations and their structural features compared with the X‐ray structure of anionic selenenate esters 14 – 16 .     

Synthesis of novel benzo[h] [1,6]naphthyridines via a rearrangement of hexahydro‐5H‐pyrrolo [2,1 ‐c] [1,4]benzodiazepines

Heating of hexahydro‐5H‐pyrrolo[2,1‐c][1,4]benzodiazepine‐2,5,11‐trione in boiling phosphoryl chloride led to a rearranged product like 3,5‐dichlorobenzo[h][1,6]naphthyridine. This structure was established from X‐ray diffraction analysis.     

On the π‐Electron Distribution in Biphenylene Analogues

The bonding situation in a series of biphenylene analogues – benzo[b]biphenylene and its dication, 4,10‐dibromobenzo[b]biphenylene, naphtho[2,3‐b]biphenylene and its dianion, benzo[a]biphenylene, (biphenylene)tricarbonylchromium, benzo[3,4]cyclobuta[1,2‐c]thiophene, benzo[3,4]cyclobuta[1,2‐c]thiophene 2‐oxide, benzo[3,4]cyclobuta[1,2‐c]thiophene 2,2‐dioxide, 4,10‐diazabenzo[b]biphenylene, biphenylene‐2,3‐dione, benzo[3,4]cyclobuta[1,2‐b]anthracene‐6,11‐dione, and 3,4‐dihydro‐2H‐benzo[3,4]cyclobuta[1,2]cycloheptene – where one of the two benzo rings of biphenylene is replaced by a different π‐system (B) was investigated on the basis of the NMR parameters of these systems. From the vicinal ¹H,¹H spin‐spin coupling constants, the electronic structure of the remaining benzo ring (A) is derived via the Q‐value method. It is found that increasing tendency of B to tolerate exocyclic double bonds at the central four‐membered ring of these systems favors increased π‐electron delocalization in the A ring. The analysis of the chemical shifts supports this conclusion. NICS (nucleus‐independent chemical shift) values as well as C,C bond lengths derived from ab initio calculations are in excellent agreement with the experimental data. The charged systems benzo[b]biphenylene dication and naphtho[2,3‐b]biphenylene dianion ( 7 ²⁻) are also studied by ¹³C NMR measurements. The charge distribution found closely resembles the predictions of the simple HMO model and reveals that 7 ²⁻ can be regarded as a benzo[3,4]cyclobuta[1,2‐b]‐substituted anthracene dianion. It is shown that the orientation of the tricarbonylchromium group in complexes of benzenoid aromatics can be derived from the vicinal ¹H,¹H coupling constants.     

Facile and simple synthesis of some new polyfunctionally heterocyclic derivatives incorporating 2‐imino‐2H‐chromene moiety

1,2‐Dihydro‐2‐imino‐6‐(2‐imino‐2H‐chromen‐3‐yl)‐1,4‐diphenyl‐pyridine‐3‐carbonitrile 4 has been synthesized and reacted with ethyl cyanoacetate to yield the new 5‐amino‐1,7‐dihydro‐2‐(2‐imino‐2H‐chromen‐3‐yl)‐7‐oxo‐1,4‐diphenyl‐1,8‐naphthyridine‐6‐carbonitrile 6 , which consider a good and available starting intermediate for synthesis of series of functionalized chromenes. So, the compound 6 was utilized as a key for the synthesis of some new pyrimido[5,4‐c][1,8]naphthyridinones, pyrido[2,3‐c][1,6]naphthyridinones, triazolo[3′,4′:1,6]triazino][5,4‐c][1,8]naphthyridinones, triazolo[2′,3′:1,6]pyrimido[4,5‐c][1,8]naphthyridinones, triazepino[6,5‐c][1,8]naphthyridinone, and triazino[5,4‐c][1,8]naphthyridinones. The structures of these compounds were established by elemental analysis, IR, MS, and NMR spectral analysis. J. Heterocyclic Chem., (2012).     

Steric and Electronic Effects on an Antibody‐Catalyzed Diels–Alder Reaction

A series of substituted thiophene dioxides was tested as diene substrates for the antibody 1E9, which was elicited with a hexachloronorbornene derivative and normally catalyzes the inverse electron‐demand Diels–Alder reaction between 2,3,4,5‐tetrachlorothiophene dioxide (TCTD) and N‐ethylmaleimide (NEM). Previous structural and computational studies had suggested that the catalytic efficiency of this system derives in part from a very snug fit between the apolar active site and the transition state of this reaction. Nevertheless, replacing all the Cl‐atoms in the hapten with Br‐atoms leads to no loss in affinity (K_d=0.1 nM ), indicating substantial conformational flexibility in the residues that line the binding pocket. Consistent with this observation, the 2,3,4,5‐tetrabromothiophene dioxide is a good substrate for the antibody (k_cat=1.8 min^?1, K_NEM=14 μM ), despite being considerably larger than TCTD. In contrast, normal electron‐demand Diels–Alder reactions between NEM and unsubstituted thiophene dioxide or 2,3,4,5‐tetramethylthiophene dioxide, which are much smaller or nearly isosteric with TCTD, respectively, are not detectably accelerated. These results show that the electronic properties of the 1E9 active site are optimized to a remarkable degree for the inverse electron‐demand Diels–Alder reaction for which it was designed. Indeed, they appear to play a more important role in catalysis than simple proximity effects.     

Amine‐Templated One‐Dimensional Metal Sulfates Including a Mixed‐Valent Fe Compound with a Half‐Kagome Structure

Organically templated metal sulfates are relatively new. Six amine‐templated transition‐metal sulfates with different types of chain structures, including a novel iron sulfate with a chain structure corresponding to one half of the kagome structure, were synthesized by hydro/solvothermal methods. Amongst the one‐dimensional metal sulfates, [C₁₀N₂H₁₀][Zn(SO₄)Cl₂] ( 1 ) is the simplest, being formed by corner‐linked ZnO₂Cl₂ and SO₄ tetrahedra. [C₆N₂H₁₈][Mn(SO₄)₂(H₂O)₂] ( 2 ) and [C₂N₂H₁₀][Ni(SO₄)₂(H₂O)₂] ( 3 ) have ladder structures comprising four‐membered rings formed by SO₄ tetrahedra and metal–oxygen octahedra, just as in the mineral kröhnkite. [C₄N₂H₁₂][V^III(OH)(SO₄)₂]?H₂O ( 4 ) and [C₄N₂H₁₂][VF₃(SO₄)] ( 5 ) exhibit chain topologies of the minerals tancoite and butlerite, respectively. The structure of [C₄N₂H₁₂][H₃O][Fe^IIIFe^II F₆(SO₄)] ( 6 ) is noteworthy in that it corresponds to half of the hexagonal kagome structure. It exhibits ferrimagnetic properties at low temperatures and the absence of frustration, unlike the mixed‐valent iron sulfate with the full kagome structure.     

Two regioisomers of condensed thioheterocyclic triazine synthesized from 6‐phenyl‐3‐thioxo‐2,3,4,5‐tetrahydro‐1,2,4‐triazin‐5‐one

In the crystal structure of 6‐phenyl‐3‐thioxo‐2,3,4,5‐tetrahydro‐1,2,4‐triazin‐5‐one, C₉H₇N₃OS, (I), the 1,2,4‐triazine moieties are connected by face‐to‐face contacts through two kinds of double hydrogen bonds (N—H...O and N—H...S), which form planar ribbons along the a axis. The ribbons are crosslinked through C—H...π interactions between the phenyl rings. The molecular structures of two regioisomeric compounds, namely 6‐phenyl‐2,3‐dihydro‐7H‐1,3‐thiazolo[3,2‐b][1,2,4]triazin‐7‐one, C₁₁H₉N₃OS, (II), and 3‐phenyl‐6,7‐dihydro‐4H‐1,3‐thiazolo[2,3‐c][1,2,4]triazin‐4‐one, C₁₁H₉N₃OS, (III), which were prepared by the condensation reaction of (I) with 1,2‐dibromoethane, have been characterized by X‐ray crystallography and spectroscopic studies. The crystal structures of (II) and (III) both show two crystallographically independent molecules. While the two compounds are isomers, the unit‐cell parameters and crystal packing are quite different and (II) has a chiral crystal structure.     

N‐alkyl‐4‐chloro‐1H‐benzo[c][1,2]thiazine‐3‐carbaldehyde‐2,2‐dioxides—New functional benzothiazine derivatives

A synthesis of N‐alkyl‐4‐chloro‐1H‐benzo[c][1,2]thiazine‐3‐carbaldehyde‐2,2‐dioxides is described. Reactivity of new β‐chloroaldehydes is investigated, a number of novel benzo[c][1,2]thiazine derivatives are synthesized and characterized using ¹H, ¹³C‐NMR, MS and elemental analysis.     

Two saccharinate complexes: [Mn(phen)2(sac)(H2O)]+·sac– and [Co(bipy)2(sac)(H2O)]+·sac–

The title saccharinate complexes, aqua[1,2‐benzisothiazol‐3(2H)‐onato 1,1‐dioxide‐N]bis(1,10‐phenanthroline‐N,N′)man­ganese(II) 1,2‐benz­isothia­zol‐3(2H)‐onate 1,1‐dioxide,[Mn(C₇H₄NO₃S)(C₁₂H₈N₂)₂(H₂O)](C₇H₄NO₃S), and aqua[1,2‐benz­iso­thiazol‐3(2H)‐onato 1,1‐dioxide‐N]­bis­(2,2′‐bi­pyri­dine‐N,N′)­cobalt(II) 1,2‐benz­iso­thia­zol‐3(2H)‐onate 1,1‐di­oxide, [Co­(C₇H₄NO₃S)­(C₁₀H₈N₂)₂­(H₂O)]­(C₇H₄NO₃S), have been prepared and their crystal structures determined at 150 K. The structure of the manganese complex consists of repeated alternating [Mn(phen)₂(sac)(H₂O)]⁺ cations and non‐coordinated saccharinate anions. The water molecule, bound to manganese as part of a slightly distorted octahedral arrangement, is hydrogen bonded to an O atom of the SO₂ group in the saccharinate counter‐ion. In contrast, the cobalt complex has one pseudo‐octahedral [Co(bipy)₂(sac)(H₂O)]⁺ cation, with the cobalt‐bound water molecule hydrogen bonded to the N atom of the accompanying free saccharinate anion.     

Selenium heterocycles XLIV. Syntheses of 8,9‐dihydro‐1,2,3‐thiadiazolo[4,5‐a]‐4,7‐dihydroxynaphthalene and 1,2,3‐selenadiazolo[4,5‐a]‐4,7‐dimethoxynaphthalene

The reaction of thionyl chloride with the semicarbazone 2 gave 4,5‐dihydro‐6,9‐dihydroxynaphtho‐[1,2‐d][1,2,3]thiadiazole ( 3 ) instead of 4,5‐dihydro‐6,9‐dimethyoxynaphtho[1,2‐d][1,2,3]thiadiazole ( 4 ). Selenium dioxide oxidation of compound 2 gave 4,5‐dihydro‐6,9‐dimethyoxynaphtho[1,2‐d][1,2,3]selenadiazole ( 5 ). Oxidation of compound 5 with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone afforded 6,9‐dimethyoxynaphtho[1,2‐d][1,2,3]selenadiazole ( 6 ).     

Efficient Synthesis and Properties of Single‐Crystalline [SnTe4]4− Salts

Single‐crystalline K⁺, Rb⁺, and Cs⁺ salts of the ortho‐tellurostannate anion have been prepared by a very efficient fusing/extraction/evaporation method. The resulting compounds with the general composition [A₄(H₂O)_n][SnTe₄] can be transferred into mixed H₂O/en solvates by solving the hydrates in 1,2‐diaminoethane (en) and ensuing layering by toluene. A mixed Rb⁺/Ba²⁺ salt results from a partial cation exchange of the Rb⁺ hydrate phase in solution. All hydrates react to polytellurides when exposed to air and represent useful starting materials for the synthesis of transition metal complexes with [SnTe₄]^4? groups as binary main group elemental ligands. [K₄(H₂O)_0.5][SnTe₄] ( 1 ), [Rb₄(H₂O)₂][SnTe₄] ( 2 ), [Cs₄(H₂O)₂][SnTe₄] ( 3 ), [K₄(H₂O)(en)][SnTe₄] ( 4 ), [Rb₄(H₂O)_0.67(en)_0.33][SnTe₄] ( 5 ), [Cs₄(H₂O)_0.5(en)_0.5][SnTe₄] ( 6 ), and [Rb₂Ba(H₂O)₁₁][SnTe₄] ( 7 ) were characterized by means of X‐ray diffractometry and optical absorption spectroscopy.