Preparation of alpha-diazocarbonyl compounds from beta-lapachone derivatives and other 1,2-naphthoquinones: use of the 2D NMR 1H,15N and 1H,13C HMBC techniques in assigning regiochemistry

The assignment of the diazo site in products of the reaction of p-toluenesulfonylhydrazine with beta-lapachone, 3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione, and other 1,2-naphthoquinones in methanol solution at room temperature has been accomplished using 1H,13C HMBC and 1H,15N HMBC NMR experiments. Only one diazo-naphthalenone product was isolated in yields ranging from 50-100% from each reaction. The site of diazo substitution of beta-lapachone and derivatives is the 1-position, in contrast to substitution at the 2-position in 4-MeO-1,2-naphthoquinone. Steric factors, rather than electronic factors, control the reaction site. Along with 2-diazo-1(2H)-naphthalenone, an additional product isolated from the reaction of p-toluenesulfonylhydrazide with 1,2-naphthoquinone was 2-diazo-4-hydroxy-1(2H)-naphthalenone. Confirmation of the formation of 6-diazo-2,2-dimethyl-2,3,4,6-tetrahydro-2H-benzo[h]cromen-5-one, obtained from beta-lapachone, was achieved using single crystal X-ray diffraction.     

Efficient solvent-free synthesis of thiazolidin-4-ones from phenylhydrazine and 2,4-dinitrophenylhydrazine

An efficient solvent-free synthesis of thiazolidinones from reaction of mercaptoacetic acid, aldehydes (benzaldehyde and valeraldehyde) or ketones (cyclopentanone and cyclohexanone), and hydrazines (phenylhydrazine and 2,4-dinitrophenylhydrazine) is reported. The compounds were generally characterized by spectroscopic techniques and specifically for 2-cyclohexanyl-3-(N-phenyl)-1,3-thiazolidin-4-one by X-ray crystallography.     

4,4′‐Sulfonyl­bis­[N‐(4‐nitro­phenyl­methyl­ene)­benzen­amine]: whole‐mol­ecule disorder

The crystal structure of the title compound, C₂₆H₁₈N₄O₆S, determined from synchrotron data with a small crystal, is characterized by the presence of whole‐mol­ecule disorder. In each mol­ecule, the two planar portions are approximately perpendicular to one another and there are short intermolecular contacts between the nitro groups.     

Hydro­gen‐bonded molecular ladders in trans‐1,2‐bis(2‐nitro­anilino)­cyclo­hexane

Crystals of the title compound, C₁₈H₂₀N₄O₄, contain equal numbers of (R,R) and (S,S) mol­ecules, but these are not precise enantiomorphs, neither are they related by crystallographic symmetry; in addition, each mol­ecule exhibits approximate, but not exact, twofold rotational symmetry. There are intramolecular N—H?O hydrogen bonds [N?O 2.609 (4)–2.638 (5) Å; N—H?O 125–132°] and the mol­ecules are linked into molecular ladders by C—H?O hydrogen bonds [C?O 3.306 (6)–3.386 (6) Å; C—H?O 146–160°].     

Semiempirical studies on the interactions of dialkyldi(aquo)tin cations, [R2Sn(H2O)2]2+, with selected nucleotides

Semiempirical calculations have been carried out on the interactions of [R₂Sn(H₂O)₂]²⁺, [R = H(CH₂)_n: n = 1–8], mainly with five nucleotides, 5′‐adenosine monophosphate (5′‐AMP), but also with guanosine 5′‐monophosphate (5′‐GMP), cytidine 5′‐monophosphate (5′‐CMP), uridine‐5′‐monophosphate (5′‐UMP) and inosine 5′‐monophosphate (5′‐IMP). The preferred sites of interaction were calculated to be the ribose O2 and O3 hydroxyl oxygens and/or the phosphate oxygens, with the nitrogen sites in the bases the least attractive to the tin compounds. This is in general agreement with experimental findings. Structures of the 1:1 coordination complexes vary from distorted tetrahedral, to distorted trigonal pyramidal to distorted octahedral geometries. Copyright © 2007 John Wiley & Sons, Ltd.     

Solvated and solvent‐free forms of N,N′‐di­thio­diphthal­imide

N,N′‐Di­thio­diphthal­imide, C₁₆H₈N₂O₄S₂, crystallizes from ethyl acetate with two independent mol­ecules in the asymmetric unit, in which the N—S—S—N torsion angles are ?83.59 (19) and 92.9 (2)°. The mol­ecules are linked by C—H?O hydrogen bonds and aromatic π–π‐stacking interactions into a three‐dimensional framework. When crystallized from either di­chloro­methane or ethanol, solvates are formed in which the mol­ecules of the title compound lie across twofold rotation axes in space group C2/c, with N—S—S—N torsion angles of 93.54 (7) and 96.14 (11)°. There are no hydrogen bonds in these solvates, but the mol­ecules are linked by aromatic π–π‐stacking interactions into chains, between which there are continuous channels. Disordered solvent mol­ecules occupy these channels, which account for ca 20% of the unit‐cell volume.     

Simple Zeros of the Riemann Zeta-Function

Assuming the Riemann Hypothesis, Montgomery showed by meansof his pair correlation method that at least two-thirds of thezeros of Riemann's zeta-function are simple. Later he and Taylorimproved this to 67.25 percent and, more recently, Cheer andGoldston increased the percentage to 67.2753. Here we proveby a new method that if the Riemann and Generalized LindelöofHypotheses hold, then at least 70.3704 percent of the zerosare simple and at least 84.5679 percent are distinct. Our methoduses mean value estimates for various functions defined by Dirichletseries sampled at the zeros of the Riemann zeta-function. 1991Mathematics Subject Classification: 11M26.     

2,3‐Dihydro‐3,3‐dimethylspiro[1H‐4‐oxanthracene‐5,2′‐oxiran]‐10(5H)‐one

The central six‐membered ring in the title compound, C₁₆H₁₆O₃, is almost planar (and almost coplanar with the aromatic ring), despite one of its C atoms being formally sp³ hybridized. The planarity is a consequence of the C atom at the centre of the spiro­cyclic system also being part of the three‐membered epoxide ring. The mol­ecules are linked by π–­π and C—H?π interactions.