Origin of the stereo- and regioselectivities in the Diels-Alder reactions of azaphospholes: a DFT investigation

Computations of the Diels-Alder (DA) reactions of azaphosphole representative namely, thiazolo[3,2-d][1,4,2]diazaphosphole with 1,3-butadiene and isoprene at the density functional theory level reveal concerted mechanisms via asynchronous transition states. The activation energies (B3LYP/6-311++G**// B3LYP/6-311G**), 16-19 kcal mol⁻¹, are much smaller than the value (32.57 kcal mol⁻¹) calculated for the DA reaction of the non-phosphorus analogue, imidazo[2,1-b]thiazole with 1,3-butadiene. An electron-withdrawing group at the 3-position of the dienophile enhances both stereo- and regioselectivities, which agree nicely with the experimental values. Inclusion of solvent effect (PCM model) reveals that the stereo- and regioselectivities are not affected appreciably. The relative stabilities of the transition structures corresponding to the endo/exo stereoisomers and meta (P/Me, 1:3)/para (P/Me, 1:4) regioisomers have been rationalized on the basis of the secondary molecular orbital interactions.     

Synthesis of some new fluorine containing 3-dialkylaminomethyl indoles, 3-indolylglyoxamides and tryptamines

Several new 2-(fluoroaryl)-3-dialkylaminomethylindoles, 3-acetyl-2-(fluoroaryl)-indoles, 2-(fluoroaryl)-3-indolylglyoxamides and corresponding tryptamines have been prepared as possible psychopharmacological agents. 2-(Fluoroaryl)-indoles have been synthesized by theFischer indole synthesis. 2-(Fluoroaryl)-indoles on treatment with oxalyl chloride and subsequent reaction with amines, gave 2-(fluoroaryl)-3-indolylglyoxamides. Some of these indolylglyoxamides were reducted with lithium aluminium hydride, to the corresponding tryptamines. 2-(Fluoroaryl)-indoles when subjected toMannich reaction afforded 3-dialkylaminomethyl-2-(fluoroaryl)-indoles. All these new compounds have been characterized by IR spectral studies.Possible Psychopharmacological Agents, Part XII, Part XI, J. Indian. Chem. Soc.57, 423 (1980).     

Synthesis and anti-tumor activity of β-C-glycoside analogs of the immunostimulant KRN7000

A ring-closing metathesis approach was employed for the synthesis of a β-C-glycoside analog of the immunostimulant KRN7000. The protected C-glycosyl amino acid derivative 18 was converted to amino-olefin 20, and osmylation served to install the diol unit as a mixture of separable syn and anti isomers. Deprotection to the hydroxy-amine 21 was followed by N-acylation and debenzylation to deliver the target compound 5.     

Synthesis and electronic,magnetic and E.s.r. studies of some bimetallic alkoxides of copper(II) with niobium(V) and Tantalum(V)

Summary Novel bimetallic alkoxides of copper(II) of the type Cu[M(OPr-i)₆]₂ (M = Nb or Ta) have been synthesised by the interaction of CuCl₂ (1 mol) with K[M(OPr-i)₆] (2 mol). These bimetallic isopropoxides undergo facile alcohol interchange with primary alcohols such as MeOH, EtOH,n-PrOH andn-BuOH. However, witht-BuOH, the reaction cannot be driven to completion even under prolonged continuous azeotropic fractionation of the liberatedi-PrOH and the final product corresponded in analysis to Cu[Ta(OPr-i)₂(OBu-t)₄]₂.I.r., electronic and electron spin resonance spectral and magnetic susceptibility measurements indicate a distorted octahedralD _4h geometry for copper(II) in these bimetallic alkoxides.     

Second-sphere coordination in hexaamminecobalt(III) salt with organic sulphonate anion: Synthesis, characterisation and X-ray crystal structure of [Co(NH3)6](CH3SO3)3

Reaction of hexaamminecobalt(III) chloride with the silver salt of methanesulphonic acid in aqueous medium (1:3 molar ratio) forms hexaamminecobalt(III) methanesulphonate, [Co(NH₃)₆](CH₃SO₃)₃, in high yield. This cobalt(III) complex has been characterized by spectroscopic techniques (UV/visible, IR and NMR) and its solubility product determined. The X-ray crystal structure shows that the [Co(NH₃)₆]³⁺ cations interact at the second sphere by sharing edges with the anions, via N–H  O hydrogen bonds. The structure is related to that of [Co(NH₃)₆]Cl(CH₃SO₃)₂, but is modified to accommodate additional anions in place of Cl⁻.     

Hydroxymethylation and cyanoethylation of nitroimidazoles

A series of nitroimidazoles were subjected to hydroxymethylations under a variety of conditions. Hydroxymethylation of 1-(2-hydroxyethyl), 1-(2-acetoxyethyl), and 1-(2-chloroethyl) substituted 5-nitroimidazoles with paraformaldehyde in dimethyl sulfoxide yielded the respective 2-hydroxymethyl analogs (5–7). However, attempts to hydroxymethylate 1-(2-hydroxyethyl), 1-(2-acetoxyethyl), 1-(2-cyanoethyl) substituted 4-nitroimidazoles and 1-(2-hydroxyethyl)-2-nitroimidazole were unsuccessful. Treatment of 1-(2-acetoxyethyl)-5-nitro-2-imidazolecar-baldehyde(10) with hydroxylamine-O-sulfonic acid afforded a mixture of corresponding 2-carbonitrile (12) and 2-(N-hydroxy)carboximidamide (13). Hydrolysis of 10 with ethanolic hydrochloric acid yielded 8-ethoxy-5,6-dihydro-3-nitro-8H-imidazo[2,1-c] [1,4]oxazine (11) which, on subsequent reaction with hydroxylamine-O-sulfonic acid, afforded 1-(2-hydroxyethyl)-5-nitroimidazole-2-(N-hydroxy)carboximidamide (15). Reaction of 4(5)-nitroimidazole with chloropropionitrile produced a mixture of the isomeric 1-(2-cyanoethyl) substituted 4- and 5-nitroimidazoles. Treatment of 2,4(5)-dinitroímidazole with chloropropionitrile afforded a mixture of 4(5)-chloro-5(4)-nitroimidazole and 1-(2-cyanoethyl)-4-nitro-5-chloroimidazoIe. Reaction of nitroimidazoles with acrylonitrile in the presence of Triton B yielded the corresponding 1-(2-cyanoethyl) substituted derivatives.     

Kinetics and mechanisms of oxidation by metalions. Part XI(1). Kinetics of the osmium(VIII)-catalysed oxidation of glycols by alkaline hexacyanoferrate(III)

Summary The kinetics of the Os^VIII-catalysed oxidation of glycols by alkaline hexacyanoferrate(III) ion exhibits zerothorder dependence in [Fe(CN) ₆ ^3– ] and first-order dependence in [OsO₄]. The order with respect to glycols is less than unity, whereas the rate dependence on [OH^–] is a combination of two rate constants; one independent of and the other first-order in [OH^–]. These observations are commensurate with a mechanism in which two complexes, [OsO₄(H₂O)G]^– and [OsO₄(OH)G]^2–, are formed either from [OsO₄(H₂O)(OH)]^– or [OsO₄(OH)₂]^2– and the glycol GH, or by [OsO₄(H₂O)₂] and [OsO₄(H₂O)(OH)]^– and the glycolate ion, G^–, which is in equilibrium with the glycol GH through the reaction between GH and OH^–. Hence there is an ambiguity about the true path for the formation of the two Os^VIII-glycol complexes. A reversal in the reactivity order of glycols in the two rate-determining steps, despite the common attack of OH^– ion on the two species of Os^VIII-complexes, indicates that the two complexes are structurally different because S changes from the negative (corresponding to k₁₁) to positive (related to k₂).     

Electrochemical detection of amino acids at carbon nanotube and nickel-carbon nanotube modified electrodes

The oxidation and enhanced detection of traditionally 'non-electroactive' amino acids at a single-wall carbon nanotube (SWNT) surface and at a nickel hydroxide film electrochemically deposited and generated upon the SWNT layer is reported. Different CNT are compared, with Nafion-dispersed SWNT offering the most favorable layer for constant-potential amperometric detection. Factors affecting the oxidation process, including the pH or applied potential, are assessed. The response of the SWNT-Nafion coated electrode compares favorably with that of copper and nickel disk electrodes under flow injection analysis (FIA) conditions. The electrodeposition of nickel onto the SWNT-Nafion layer (Ni-CNT) led to a dramatic enhancement of the analytical response (vs. that observed at the SWNT or nickel electrodes alone). The oxidative process at the Ni(OH)(2) layer has been studied and the increase in sensitivity rationalized. In the presence of amino acid the Ni-CNT layer undergoes an electrocatalytic process in which the amino acid reduces the newly formed NiO(OH) species. Furthermore, the attractive response of both the CNT and Ni-CNT layers has allowed these electrodes to be used for constant-potential FIA of various amino acids and indicates great promise for monitoring chromatographic effluents. Once again an improved signal was observed at the Ni-CNT electrode compared to nickel deposited upon a bare glassy carbon electrode (Ni-GC).     

Synthesis and characterisation of some new cyanonitrosyl chromium(l) complexes with phenetidines and anisidines

Summary A new series of cyano-substituted nitrosylchromium(I) complexes having octahedral stereochemistry around the metal ion, and of general formula, [CrNO(CN)₂(L)₂(H₂O)] (L =o-,m- andp-phenetidines oro-,m-, andp-anisidines) have been isolated in the solid state by interaction of potassium pentacy-anonitrosylchromate(I) monohydrate with the appropriately substituted aniline. The complexes, which have been characterised by elemental analysis, conductance, molecular weight determination, magnetic measurements, e.s.r. and i.r. spectral studies, contain chromium(I) in a low-spin d⁵-configuration.