An efficient synthesis of 7-hydroxy-2,6-dimethylchromeno[3,4-d]oxazol-4-one—a protected fragment of novenamine

The high-yielding six-step synthesis of 7-hydroxy-2,6-dimethylchromeno[3,4-d]oxazol-4-one 17 from commercially available 2,4-dihydroxy-3-methylacetophenone is described. Coumarin 17 constitutes a useful synthon for coumarin antibiotic synthesis. A new methodology for oxazole formation applicable to 3-aminocoumarins has been developed, and a mechanistic rationalization is proposed.     

Synthesis of 3-hexahelicenol and its transformation to 3-hexahelicenylamines,diphenylphosphine, methyl carboxylate,and dimethylthiocarbamate

A nonphotochemical synthetic route to 3-hexahelicenol is reported. It involves a key [2+2+2] cycloisomerization of CH(3)O-substituted triyne that is readily available from 1-methoxy-3-methylbenzene and 1-bromo-2-(bromomethyl)naphthalene. Further functional group transformations led to 3-CO(2)CH(3), 3-NH(2), 3-PPh(2), and 3-SC(O)N(CH(3))(2) substituted hexahelicenes.     

Kinetics of radical telomerization of vinylidene fluoride in the presence of CCl3Z chain transfer agents

The kinetics of radical telomerization of VDF at 141 °C, initiated by ditertbutylperoxide, in the presence of three chain transfer agents (CTAs), HCCl₃, CCl₄ and CCl₃Br, are presented. The values of the chain transfer constants were assessed as 35, 0.25 and 0.06 at 141 °C for CCl₃Br, CCl₄ and HCCl₃, respectively. The values of the degree of polymerization (DP_n) were obtained for each CTA and were compared for the same CTA concentration. Hence, CCl₃Br behaved as an efficient CTA towards VDF and usually afforded the monoadduct selectively, but in certain conditions the VDF diadduct can also be produced. In contrast, HCCl₃ was not so efficient since a polymeric structure was identified as the major product.     

Synthesis and Transformation of Methyl 2‐(6‐Hydroxy‐2‐phenylpyrimidin‐4‐yl)acetate: Simple Preparation of Pyrimidines with Heterocyclic Substituents

A simple and efficient synthesis of four new substituted pyrimidines, compounds 9a – d , from the title compound 3 is described. Conversion of 3 to methyl (E)‐3‐(dimethylamino)‐2‐(6‐methoxy‐2‐phenylpyrimidin‐4‐yl)prop‐2‐enoate ( 4 ), followed by condensation with various dinucleophiles according to the ‘enaminone methodology’, afforded the target compounds 9 in medium‐to‐good yields.     

On the nature of the fluorescent state of methylated indole derivatives

A quantitative study has been made of the solvent effects on the fluorescence properties of 1- and 3-methyl indole, with the aim of further understanding the origin of the unusually large Stokes shift in polar solvents. For the derivatives considered here the fluorescence transition probability is decreased in solvents of moderate and high polarities, and the spectrum shifts to the red. The data (in two-component, solute and solvent, systems) can be interpreted on the basis of the stabilisation, by solvent-solute relaxation, of a state with an increased charge-transfer character, relative to the initially excited state. Å consideration of the decay data for other indole derivatives suggests that this state has its origin in the ¹L₄ state (S₂ in non-polar media). Thus we conclude that the appropriate label of the fluorescent state of many substituted indoles in polar solvents is ¹L_a/CT. This is consistent with the observed solvent, temperature, time and substituent dependence of the decay kinetics of these derivatives.     

A Concise, Enantioselective Synthesis of (-)- and (+)-Hongconin

Optically pure enone 9c, available in three steps from known 6-deoxy D-galactal derivative 7b, reacts with cyanophthalide 6 to directly afford the natural product (-)-hongconin (1), a compound from traditional Chinese medicine recently shown to exhibit antianginal activity. The enantiomer of 1 and its (+)-cis-diastereomer were also synthesized in a parallel fashion from the L-sugar counterpart. The use of C-glycoside Michael acceptors, as opposed to their O-glycoside counterparts, represents a potentially useful simplification of phthalide annulation methodology in synthesizing numerous other such optically pure isochromanquinoids, since it obviates the inconvenience of additional steps late in the synthetic scheme associated with reductive manipulation of a remaining acetal moiety into the desired pyran ring substituent.     

Complexation of aluminate anion by bis-tris in aqueous media at 25–50°C

Gibbsite, Al(OH)₃, solubility studies in aqueous NaCl solutions at pH 9 demonstrate that the aluminate anion forms a strong complex with the neutral Bis-tris molecule 2,2-Bis(hydroxymethyl)-2,2,2-nitrilotriethanol, at low temperatures. The logarithm of the molal concentration quotient for the reaction

Suggested calculations using transition density matrices

It is suggested that certain transition density matrices, N-representable in a limit, be used in a variational calculation. It is noted that such trial matrices should yield reasonable values for the ground state energies of small atoms or molecules provided a set of overlap integrals is maximised.

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Zusammenfassung Es wird vorgeschlagen, bestimmte Übergangsdichtematrizen, die im Limit N-darstellbar sind, in einer Variationsrechnung zu benutzen. Es wird festgestellt, daß solche Näherungsmatrizen gute Werte für die Energie des Grundzustandes kleiner Atome oder Moleküle geben sollten, falls im Satz von Überlappungsintegralen maximiert wird.

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Résumé On propose d'utiliser dans un calcul variationnel certaines matrices densité de transition, N représentables à la limite. Ces matrices d'essai devraient fournir des valeurs raissonnables pour l'énergie de l'état fondamental dans les petits atomes et les petites molécules à condition de maximiser un ensemble d'intégrales de recouvrement.

     

Application de la radiopolarographie a l'étude dequelques éléments à l'échelle des indicateurs

Basic equations of classical polarography are transposed and tested withmanganese and europium at tracer scale. Using the previously presented automatic system, standard dispersion for experimental points is about 3% and residual activity before the wave 3±2% compared with diffusion activity A_d. Results with manganese in 10^?3M ≤[LiCl]≤10^?1M and 2≤pH≤4 solutions, give an experimental yield about 100%, E_1/2=?1.47 V/SCE and α?0.85. The last values agree with results achieved at a weighable scale. For potentials <?2.00 V/SCE a screening effect with supporting electrolyte ions is observed. The screening effect influence on the diffusion coefficient is taken into consideration and results for europium (R?100%, E_1/2??1.95 V/ECS, α=1 at pH 2.7) are in good agreement with the literature. Radiopolarograms for Mn and Eu and mixtures of both are similar. Thus the range of polarographic analysis is enlarged.     

Acidic aqueous decomposition of thiocyanogen

The aqueous reaction of acidic Cl2 with excess SCN- rapidly generates a UV-absorbing intermediate identified as an equilibrium mixture of thiocyanogen, (SCN)2, and trithiocyanate, (SCN)3(-). The decomposition of this mixture can be described as 3(SCN)2 + 4H2O --> 5HSCN + H2SO4 + HCN. Under our conditions the decomposition is sufficiently slow that its kinetics can be studied using standard stopped-flow methodology. Over the pH range 0-2 the decomposition rate law is -d[(SCN)2]/dt = (3/2)[k(disp)K(hyd)2[(SCN)2]2/([SCN-]2[H+]2 + K(SCN)3-[SCN-]3[H+]2 + K(hyd)[SCN-][H+])] with K(SCN)3(-) = 0.43 +/- 0.29 M(-1), K(hyd) = (5.66 +/- 0.77) x 10(-4) M2, and k(disp) = (6.86 +/- 0.95) x 10(4) M(-1) s(-1) at 25 degrees C and micro = 1 M. The K(SCN)3(-) and K(hyd) terms are significant enhancements relative to one of the rate laws conventionally cited. In the proposed mechanism, K(SCN)3(-) refers to the formation of (SCN)3(-) by association of SCN- with (SCN)2, K(hyd) refers to the hydrolysis of (SCN)2 to form HOSCN, and k(disp) is the rate constant for the bimolecular irreversible disproportionation of HOSCN, which leads ultimately to SO4(2-) and HCN. Ab initio calculations support the values of K(SCN)3(-) and K(hyd) reported herein. The high value for k(disp) indicates that HOSCN is a short-lived transient, while the magnitude of K(hyd) provides information on its thermodynamic stability. These results bear on the physiological role of enzymes that catalyze the oxidation of SCN- such as salivary peroxidase and myeloperoxidase.