An efficient synthesis of 5-bromo-2-methoxy-6-methylaminopyridine-3carboxylic acid

An efficient synthesis of 5-bromo-2-methoxy-6-methylaminopyridine-3-carboxylic acid (1), a carboxylic acid moiety of a potent dopamine D2 and D3 and serotonin-3 (5-HT3) receptors antagonist, (R)-5-bromo-N-(1-ethyl-4-methylhexahydro-1 ,4-diazepin-6-yl)-2-methoxy-6-methylaminopyridine-3-carboxamide, is described. Reaction of methyl 2,6-difluoropyridine-3-carboxylate (12) with methylamine in EtOH at -25 degrees C gave a mixture of methyl 2-fluoro-6-methylaminopyridine-3-carboxylate (13) and the regioisomer 14 in a ratio of 57 : 43. On the other hand, reaction of 12 and methyl 2,6-dichloropyridine-3-carboxylate (16) with sodium methoxide in tetrahydrofuran (THF) and CH2Cl2 provided the 2-methoxypyridine-3-carboxylic esters 20 and 23, respectively, as main products. Similar reaction of 16 in N,N-dimethylformamide (DMF) and MeOH proved to be highly regioselective for the 6-position. A much greater regioselectivity for substitution at the 6-position (>97%) was observed when 16 was treated with 4-methylbenzenethiolate anion in DMF (quantitative yield). After methoxylation of methyl 2-chloro-6-(4-methylbenzenethio)pyridine-3-carboxylate (25b) and successive oxidation of the 6-benzenethio moiety, nucleophilic substitution of the sulfoxide derivative 28 with methylamine gave the 6-methylamino derivative 8. Finally, bromination of 8 and alkaline hydrolysis produced the desired product 1 in an overall yield of 67%.     

Third virial coefficient of polystyrene in benzene

Second virial coefficients A₂ and third virial coefficients A₃ for benzene solutions of ten polystyrene fractions ranging in weight-average molecular weight M_w from 10⁴ to 2 × 10⁷ at 25°C were determined by light scattering. The third coefficient is represented approximately by A₃ = 8.0 × 10^?6 M mol g^?3 cm⁶ for M_w above 10⁵. In this molecular weight region, the factor g defined by A₃/AM_w/ This trend of g is consistent with predictions of early two-parameter theories but not with those of renormalization group theories. In particular, quantitative agreement is observed between the present experiments (for M_w ? 2 × 10⁵) and the mean-field two-parameter theory of Stockmayer and Casassa.     

A novel calamitic mesophase semiconductor with the fastest mobility of charged carriers: 1,4-di(5'-octyl-2'-thienyl)benzene

The carrier mobility of highly ordered lamellar mesophases was evaluated by a Time-of-Flight (TOF) method for mesogenic 1,4-di(5'-octyl-2'-thienyl)benzene (8-TPT-8) to reveal the fastest drift mobility (0.1 cm(2) V(-1) s(-1) for the lowest temperature mesophase) in calamitic liquid crystals reported to date.     

On the spontaneous electro-optic effect in triglycine sulphate crystals with L-threonine admixture

The temperature and spectral dependences of the coefficients R _i2* of the quadratic electro-optic effect (EOE) in triglycine sulphate crystals with 5% L-threonine admixture have been calculated using the temperature and spectral dependences of the refractive indices n _i . It is established that the coefficients R _i2* of the admixture-containing triglycine sulphate crystals exhibit weak spectral and temperature dependences. In the polar direction, R _i2* are substantially different from the coefficients of admixture-free triglycine sulphate crystals. This indicates the occurrence of a bias field, the predominant orientation of the dipole moment of the polar defect, and a decrease in the spontaneous polarization in admixture-containing crystals.     

On Isotropic Points in K2SO4 Impurity Crystals

Optics and Spectroscopy - The temperature, spectral and baric dependences of birefringence Δni of potassium sulfate crystals doped with 1.7% of copper are studied. It is established that the...     

Mesomorphic properties of a tetraphenylporphyrin metallomesogen with a weak hydrogen bond interaction between axial ligands: dihydroxo[5,10,15,20-tetrakis(4-n-dodecylphenyl)porphinato]silicon(IV)

A new metallomesogen, the dihydroxo[5,10,15,20-tetrakis(4-n-dodecylphenyl)porphinato]silicon(IV) complex, C₁₂TPPSi(OH)₂, was synthesized and its mesomorphism was investigated in terms of the axial hydrogen bond interaction in the stacked columnar structure. It was found that this compound exhibits a 3D plastic lamellar mesophase with a columnar structure, and the axial hydroxyl groups are connected by a very weak hydrogen bond interaction in the column. This causes a dramatic increase of the clearing point for the mesophase, even though the stacking periodicity is far larger (c. 9?Å) than that typically found for a columnar meosphase (c. 3.5?Å).     

Intramolecular Photocyclization of 2‐Acylphenyl Methacrylates: a Convenient Access to 4,5‐Dihydro‐1,4‐epoxy‐2‐benzoxepin‐3(1H)‐ones (= Benzo[c]‐6,8‐dioxabicyclo[3.2.1]octan‐7‐ones

The photochemical reactions of 2‐acylphenyl methacrylates (= 2‐acylphenyl 2‐methylprop‐2‐enoates) 1 were investigated. Irradiation of 2‐acylphenyl methacrylates 1a – d in MeCN gave the tricyclic lactones 2a – d in good yields, together with a small amount of O CO bond cleavage product, the 2‐acylphenols 3a – d (Scheme 2, Table). The formation of the tricyclic lactones 2 probably follows a mechanism involving a 1,7‐diradical through ζ‐H abstraction (1,8‐H transfer) by the excited carbonyl O‐atom (Scheme 3). Irradiation of 2‐acylphenyl tiglate (= 2‐acylphenyl (2E)‐2‐methylbut‐2‐enoate) 1e and 2‐acylphenyl methacrylates 1g – i , substituted by a MeO group (δ‐H) at the 3,5‐positions of the phenyl group, also gave the tricyclic lactones 2e and 2g – i , but in low yields. On the other hand, no H‐abstraction products were observed on irridation of 2‐(ethoxycarbonyl)phenyl methacrylate 1f , of 2‐acylphenyl methacrylate 1j which is substituted by a Me group (γ‐H) at the 3,5‐positions of the phenyl group, and of 1k with an OH group at the 3‐position of the phenyl group.     

Acetate reduction synthesis of Sr2Si5N8:Eu phosphor and its luminescence properties

A novel synthesis method was developed for the efficient red phosphor, Eu²⁺-activated Sr₂Si₅N₈, by employing the strontium acetate as both the reducing agent and strontium source. The phase purity of final product was strongly dependent on the heating rate of the precursors. Sr₂Si₅N₈:Eu²⁺ (2 at%) phosphor presented a broadband excitation spectrum in the range 300–500 nm, matching well with the blue emission (400/460 nm) of current InGaN light-emitting diodes (LEDs). The red emission peaking at 619 nm gave the relatively high (about 155%) intensity compared with the Y₃Al₅O₁₂ (YAG) (P46-Y3) standard phosphor. In addition, the saturated chromatic coordinates (0.638, 0.359) allowed it a promising candidate as a red phosphor in white LEDs application for illumination or display.