Transformations of lignans. Part 11: Oxidation of diphyllin with hypervalent iodine reagents and reductive reactions of a resulting 1-methoxy-1-aryl-4-oxonaphthalene lactone

Treatment of diphyllin 4 with phenyliodonium diacetate (PIDA) in methanol affords a 1-methoxy-1-aryl-4-oxonaphthalene lactone 6. Reduction of 6 with lithium aluminium hydride yields, inter alia, 3,4-dihydrodiphyllin 13, while reaction with sodium in ethanol yields 8 as a major product. These reactions illustrate that selective oxidation followed by reduction provides a facile route for the conversion of a 1-arylnaphthalene lactone to novel functionalised naphthalene and dihydronaphthalene derivatives. Of particular interest is that the oxidation indirectly activates the methylene position (C-10) of the γ-lactone, which may then potentially be substituted to give a new series of lignans. Reaction of 6 with hydroxylamine and benzyloxyamine also proceeds by way of initial attack at C-10.     

Molecular adducts between a few phenolic donors and pi-acceptors in solid-state

Electron donor-acceptor molecular complexes of a few phenolic donors with some quinonoid and tetracyanoethylene acceptors have been prepared by two different methods, i.e., by simple grinding of the respective component pair in the solid-state and in solution. Both the methods yielded identical dark colored 1:1 stoichiometric complexes. Spectral studies revealed that the complexes are ionic in nature. The g values obtained in ESR spectral studies for all these molecular adducts vary between 2.000 and 2.022, confirming the free radical nature of the adducts. The electronic absorption spectral studies proved that the donor-acceptor complexes formed initially, exhibit new electronic transitions at longer wavelengths, are less stable and disassociate readily into ionic type of adducts. The absorption maximum at longer wavelengths, i.e. >or=550 nm, are assigned to the charge transfer complexes, while the new transition at around 410 +/- 5 nm is attributed to the anion radical of the adducts. The ease of complexation not only depends on the ionization potential and electron affinities of the phenolic donors and the acceptors but is also structure sensitive. Complexation is confirmed by the shift in IR absorption of the phenolic hydroxyl group and the carbonyl group of quinone acceptors and the cyano group of tetracyanoethylene. Proton magnetic resonance studies indicate an interaction between the phenolic donors and acceptors on basis of the altered chemical shifts. Further, IR and NMR studies show that the stability of the adducts is governed not only by the charge transfer interaction but also by hydrogen bonding.     

Characterization of clinohumite by selected spectroscopic methods

Clinohumite, a humite group mineral, originated from Pamir Mountains, USSR, is used in the present work. Optical absorption, electron paramagnetic resonance (EPR), near infrared (NIR) and M?ssbauer techniques are used in the characterization of the mineral sample. The optical absorption spectrum indicates that Fe(II) impurity is present in two sites with distorted octahedral structure. NIR results are attributed to water fundamentals. EPR studies on powder sample confirm the presence of Mn(II) in three different sites and also an iron impurity. M?ssbauer studies confirm the presence of iron impurity in two different sites.     

Synthesis and spectral investigations of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) complexes of new polydentate ligands containing a 1,8-naphthyridine moiety

2-(o-Hydroxyphenyl)-1,8-naphthyridine (HN), 2-(4-hydroxy-6-methylpyran-2-one-3-yl)-1,8-naphthyridine (HMPN) and 2-(benzimidazol-2-yl)-1,8-naphthyridine(BN) react with acetates of Mn(II), Co(II), Ni(II), Cu(II) and Zn(II) to yield metal ion complexes of definite composition. These compounds were characterized by elemental analyses, molar conductivity, magnetic susceptibility measurements, thermal studies, IR, UV-visible, NMR and mass spectral investigations. The complexes are found to have the formulae [M(HN)2(H2O)2], [M(HMPN)2(H2O)2] and [M(BN)2(OAc)2], respectively.     

Functionalized chiral vinyl aminosulfoxonium salts: asymmetric synthesis and application to the synthesis of enantiopure unsaturated prolines, beta,gamma-dehydro amino acids, and cyclopentanoid keto aminosulfoxonium ylides

Methylation of the enantiopure functionalized vinyl sulfoximines 5a-e and 14a-d followed by a F- ion or DBU-mediated isomerization of the vinyl aminosulfoxonium salts 7a-e and 15a-d, respectively, gave the allyl aminosulfoxonium salts 10a-e and 17a-d, respectively. A concomitant intramolecular substitution of the aminosulfoxonium group of 10a-e and 17a-d by the amino group afforded the unsaturated prolines 8a-e and 18a-d, respectively. The starting vinyl sulfoximines are accessible through a highly selective and stereo-complementary aminoalkylation of the corresponding sulfonimidoyl-substituted mono- and bis(allyl)titanium complexes with the imino ester 4. The vinyl aminosulfoxonium salts 34, 7a-d, and E-15c experienced upon treatment with the Cl- ion a migratory substitution with formation of the delta-chloro-beta,gamma-dehydro amino acids 36, E/Z-37a-d, and 38, respectively. A migratory substitution of the hydroxy-substituted vinyl aminosulfoxonium salts 46a and 46b furnished the delta-chloro allyl alcohols E/Z-48a and E-48b, respectively. A facile one-pot conversion of the vinyl sulfoximines 31b, 5c and 45a to the allyl chlorides 36, E/Z-37c and E/Z-48a, respectively, was achieved upon treatment with a chloroformiate. A tandem cyclization of the vinyl aminosulfoxonium salts 7b, Al-7b and 57 with LiN(H)tBu yielded the cyclopentanoid keto aminosulfoxonium ylides 54, Al-54, 59, 60 and 61, respectively. The structure of the tricyclic keto aminosulfoxonium ylide Al-54 has been determined by X-ray crystal structure analysis. Ab initio calculations and a NBO analysis of the tricyclic keto aminosulfoxonium ylide XXIII show a polar structure stabilized by electrostatic interactions between the ylidic C atom and both the carbonyl C atom and the S atom.     

Novel acetoxylation and C-C coupling reactions at unactivated positions in alpha-amino acid derivatives

[Structure: see text] Under special conditions, N-phthaloyl-alpha-amino acid amides of 8-aminoquinoline can be either acetoxylated or arylated selectively at the beta-carbon. In certain cases, arylation can be effected at the gamma-carbon.     

First enantioselective total synthesis and structure determination of the anthrapyran metabolite gamma-indomycinone

The first total synthesis of (R)-gamma-indomycinone has been achieved which allowed the determination of the configuration of the stereogenic center of natural gamma-indomycinone as (S). The approach stands out for its generality and efficiency. [reaction: see text]     

Multidimensional liquid chromatography for sample characterisation

While LC finds enormously widespread use in almost all areas of chemical science, the technique is limited as a means of identification because compounds do not elute with unique retention times. This limitation spurred the growth of hyphenated instrumental methods of analysis, such as LC-MS/MS, which because of the MS/ MS detection became a method of identification. However, techniques like LC-MS/ MS are specialised and require high initial purchase and running costs, inhibiting the more widespread growth of the technique. In an attempt to increase the separation power of LC, multi-dimensional LC was developed. This expanded the separation space and subsequently has allowed the development of methods with fingerprinting ability due to the lower probability of component overlap. The work in this study illustrates the application of 2-D LC as a means of chemical fingerprinting. We employed a sample base of various low molecular weight oligostyrenes and their diastereomers that represent a population of compounds whose selectivities in a one-dimensional separation are almost unity and hence essentially impossible to separate. Yet in a 2-D domain almost all individual components occupy unique 2-D retention times.     

Efficient method for selective introduction of substituents as C5 of isoleucine and other alpha-amino acids

[reaction: see text] A useful process for the position-selective remote bromination of N-trifluoroacetyl-alpha-amino esters is illustrated for the isoleucine case. The 5-bromoisoleucine derivative shown above can be used for the synthesis of many modified amino acids, as described herein.