Dimetalated tertiary succinamides. Synthesis of several classes of lignans including the mammalian urinary lignas enterolactone and enterodiol

Reaction of dimetalated succinamides with benzyl halides and aromatic aldehydes provides short routes to diverse lignan natural products $\text{2}$, $\text{3}$, and $\text{4a}$, including the human urinary metabolites ($\text{3d}$) and ($\text{2e}$).     

Solid solution formation in chalcopyrite systems of the type AgInX2AgMIIIX2 where M = Al,Ga, and X = S,Se

Previous (1) work on ternary chalcopyrite solid solution formation has shown that the difference in end point axial ratios ($\text{Δc}\text{a}$) is an important factor in determining the extent of mutual solubility. It was concluded that when $\text{Δc}\text{a}\text{> 0.13}$ complete solid solubility will not occur. In this work it is shown that complete solid solution formation in the systems AgAlS₂AgInS₂ ($\text{Δc}\text{a}\text{= 0.111}$), AgGaS₂AgInS₂ ($\text{Δc}\text{a}\text{= 0.11}$) and AgAlSe₂AgInSe₂ ($\text{Δc}\text{a}\text{= 0.112}$) does occur. This shows that the value of $\text{Δc}\text{a}\text{= 0.13}$ as an upper limit for solid solution formation can be approached closely.     

The mechanism of biomolecular methyl transfer in a methyl aminoalkanesulfonate. application of 18o isotope shifts in 13cmr spectra of sulfonic esters.

¹³Cmr spectra show complete absence of scrambling of an ¹⁸O label in $\text{1}$$\text{a}$ recovered after partial conversion to $\text{2}$$\text{a}$ thereby precluding an $\text{0}$-methylation mechanism for the bimolecular formation of $\text{2}$$\text{a}$ from $\text{1}$$\text{a}$.     

The facile (<−50°C) formation of cis-bicyclo[6.1.0]nona-2,4,6-trienes from cyclonona-1,3,5,7-tetraenes: A symmetry - forbidden reaction

The formation of the $\text{cis}$-bicyclo [6.1.0] nona-2,4,6-trienes $\text{4a}$-$\text{c}$ is not due to the sequence $\text{1}$ → $\text{2}$ → $\text{4}$, which would involve the symmetry-forbidden reaction $\text{2}$ → $\text{4}$ even at ?50°C. Rather, reaction of RX at C^4–7 of $\text{5}$, which is formed together with $\text{1}$, leads (probably via $\text{6a}$-$\text{c}$ and $\text{7a}$-$\text{c}$ to $\text{4a}$-$\text{c}$.     

Fluorocarbon derivatives of nitrogen. Part 11. Synthesis of some 2-(trifluoromethyl)imidazo[1,2-a]pyridines from trifluoroacetonitrile

3-(t-Butoxycarbonyl)-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine, prepared from trifluoroacetonitrile and pyridinium t-butoxycarbonylmethylide, reacts smoothly with trifluoroacetic acid to provide 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine-3-carboxylic acid, which gives 2-(trifluoromethyl)imidazo[1,2-$\text{a}$]-pyridine when heated. 3-Cyano-2-(trifluoromethyl)imidazo[1,2-$\text{a}$]pyridine can be obtained $\text{via}$ treatment of trifluoroacetonitrile with pyridinium cyanomethylide, which is sufficiently reactive to effect nucleophilic displacement of fluorine from pentafluoropyridine under mild conditions [→pyridinium cyano(tetrafluoro-4-pyridyl)methylide].     

Marine natural products: fistularin-1, -2 and -3 from the sponge Aplysina fistularis forma fulva

Three new high molecular weight bromotyrosine-related metabolites, $\text{3a}$, $\text{4a}$ and $\text{5a}$, were isolated from the sponge Aplysina ( Verongia) fistularis forma fulva, and their structures were determined from high resolution ¹H NMR and other spectroscopic data. The new metabolites are formally derived by combination of major segments of two known Aplysina metabolites $\text{1a}$ and $\text{2}$.     

2-cyano Δ3 piperidines vi1 : a general method for the stereoselective synthesis of cis and trans 2,6-dialkylpiperidine alkaloids

The cis 2,6-dialkylpiperidine alkaloid (±) dihydro-pinidine $\text{7b}$ and the trans alkaloid (±) solenopsin A $\text{5a}$ were synthesized from a common α-aminonitrile synthon $\text{1}$. The key step in this synthesis was the stereoselective reductive decyanation of the 1-benzyl-2cyano-2′, 6-dialkylpiperidines $\text{3a}$ and $\text{3b}$.     

A study of polytypism in AgIn5Se8 by combined electron microscopy techniques

Three different polytypes are found to exist in AgIn₅Se₈. They have been studied by means of conventional electron microscopy and diffraction as well as by high-resolution microscopy. The three different structures have tetragonal symmetry and can be derived from each other by means of periodic antiphase boundaries; they correspond to $\text{c}\text{a}\text{= 4,}\text{c}\text{a}\text{= 2}$, and $\text{c}\text{a}\text{= 1}$, respectively. Regions of $\text{c}\text{a}\text{= 4}$ often occur as microsyntactic intergrowths into $\text{c}\text{a}\text{= 2}$ areas, and a large number of nonperiodic antiphase boundaries also occur. After fast cooling from above T_c a transition state characterized by the presence of diffuse intensity has been observed and analyzed.     

Structures of simarinolide and guanepolide (x-ray analysis), new quassinoids from Simaba cf orinocensis

Simarinolide $\text{4a}$ and Guanepolide $\text{5a}$ are new quassinoids with a C₂₅ basic skeleton isolated from a member of the French Guyanan Simaroubaceae, Simaba cf orinocensis H.B.K. The structure $\text{4a}$ was established by spectral means and that of $\text{5a}$ by X-ray diffraction analysis. The previously known simarolide $\text{1}$ was also isolated.     

Synthesis of 4a-, 4e-phenyladamantanones and 2,4-o-benzenoadamantane by π-route

The acid catalysed reaction of 4-oxa-homoadamantan-5-one ($\text{1}$) with benzene yielded a mixture of 4^a-phenyladamantan-2-one ($\text{7}$), the equatorial isomer' ($\text{8}$) and 2-phenyl-2,4-o- benzenoadamantane ($\text{9}$) A plausible reaction pathway for the occurrence of $\text{9}$. is put forward. The structure of $\text{9}$, was deduced from spectroscopic data and reaction of the proposed intermediate 2,4^a-diphenyladamantan-2-ol ($\text{11}$) with acid. 2,4-o-Ben-zenoadamantane ($\text{16}$) is prepared likewise.     

Organothiometallate - alkyne addition products. The crystal and molecular structure of [(η5-C5H5)W{C(CO2Me)C(CO2Me)C(O)SMe} (CO)2]

The title compound is the final product of the reaction between dimethylacetylene dicarboxylate and [(η⁵-C₅H₅)W(SMe) (CO)₃ ]. Its molecular structure has been established by an $\text{x}$-ray analysis based on 3301 diffractometric intensities. The crystals are monoclinic, space group $\text{P}$2₁/$\text{a}$, with four molecules in a cell of dimensions $\text{a}$ = 10.323(2), $\text{b}$ = 16.016(2), $\text{c}$ = 10.437(2)», β = 103.56(2)°. After least-squares refinement $\text{R}$ = 0.036. The tungsten co-ordination is square-pyramidal, the apical site being occupied by the centroid of the cyclopentadienyl ring. The basal co-ordination sites contain two carbonyl groups and also the sulphur and σ-bonded carbon atoms of a chelating carbothiolic methyl ester ligand derived from the incoming alkyne and CO and SMe groups of the original complex. The W-S and σ-W-C bond lengths are 2.440(2) and 2.194(7)».     

Oxidation of N-hydroxyazetidines: A novel synthesis of N-acetoxy β-Lactams and four-membered cyclic nitrones

The N-hydroxyazetidines $\text{2}$ and $\text{3}$ are prepared startinfrom 2,3-dihydroazete 1-oxides ($\text{1a}$ and $\text{1b}$0 by reduction with sodium borohydride and by reaction with a nucleophile, respectively. The N-thydroxyazetidines $\text{2}$ and $\text{3}$ can be oxidized with mercury (II) oxide to the corresponding nitrones $\text{1}$; oxidation of the N-hydroxyazetidine $\text{2a}$ (unsubstituted at C-4) with $\text{two}$ equivalent of lead tetraacetate tyields the N-tacetoxy β-lactam $\text{4}$.     

Action of tert-butyl azidoformate on the conjugate bases of 1,2,3,4-tetrahydro-9H-carbazole and other indole derivatives

tert-Butyl azidoformate ($\text{2}$) reacts with the conjugate bases of $\text{3a}$, $\text{7a}$, $\text{9}$ (R¹ = R² = CH₃), and $\text{9}$ (R¹ = CH₃, R² = H) to give products [$\text{4}$, $\text{8}$, $\text{12}$, and $\text{14}$, respectively] in addition to the expected N-(tert-butoxycarbonyl)indole derivatives.     

Contiguous concerted participation in the rearrangement of anti-tricyclo[4.2.1.1.2,5]deca-3,7,-diene-9,10-diol,a highly hindered system.

The acid catalysed peclppangement of anti-tricyclo[4.1.1.^2,5]deca-3,7-diene-9, 10-diol ($\text{1a}$) to $\text{2a}$ is shown to proceed through concommitant electrophilic and nucleophilic attack on an alkene by an incipient carbonium ion and the rernaining alcohol function.     

Electrophilic substitution at the δ-methine bridge of pheophorbide a and a′

A chloro-substituted derivative was prepared from chlorophyll $\text{a}$′. The derivative was shown to be δ-chloro-methyl pheophorbide $\text{a}$ by UV/VIS, MS and ′H NMR.     

The resolution of racemic 2-alkyl-1-aminocyclopropane-1-carboxylic acids

Practical procedures for the resolution of racemic modification of (1$\text{R}$, 2$\text{S}$)-and (1$\text{S}$, 2$\text{R}$)-1-amino-2-ethylcyclopropane-1-carboxylic acid $\text{1a}$,$\text{b}$,(1$\text{R}$, 2$\text{S}$)- and (1$\text{S}$, 2$\text{R}$)-1-amino-2-methylcyclopropane-1-carboxylic acid $\text{2a}$,$\text{b}$, and (1$\text{R}$, 2$\text{R}$)- and (1$\text{S}$, 2$\text{S}$)-1-amino-2-methylcyclopropane-1-carboxylic acid $\text{3a}$,$\text{b}$ are described; the structures as $\text{1a}$,$\text{2a}$, and $\text{3a}$ were confirmed by X-ray-crystallographic methods.     

Synthesis and absolute configuration of A-factor,the inducer of streptomycin biosynthesis in inactive mutants of Streptomyces griseus

The absolute configuration at C-3 of A-factor, 2-(6-methylheptanoyl)-3-hydroxymethyl-4-butanolide $\text{1a}$, was determined to be $\text{S}$ by synthesizing(3$\text{S}$)-(+)-A-factor.     

Perhalogenmethylmercapto-heterocyclen, (VII) [1] konkurrenzreaktionen elektronenarmer,substituierter aromaten um die halogenmethylmercapto- BZW. Chlorgruppe von Cl3-nFnCSCl in starken saeuren

Electron-deficient aromatics, such as 2,5-bis(trifluoromethylmercapto)thiophene ($\text{1a}$) or (trifluoromethylmercapto)benzene ($\text{8a}$), react with F₃CSCl in the presence of F₃CSO₃ as a catalyst to give mainly 3-chloro-2,5-bis(trifluoromethylmercapto)thiophen ($\text{3a}$) and 1-chloro-4- or 2-(trifluoromethylmercapto)benzene ($\text{10}$, respectively. This reaction competes with the one expected to result in 2,3,5-tris(trifluoromethylmercapto)thiophene ($\text{2a}$) and 1,4- and 1,2-bis(trifluoromethylmercapto)benzene ($\text{9}$,$\text{9′}$), respectively. Further reactions of deactivated aromatics with Cl_3-nF_nCSCl show that the chlorine substitution is in general catalysed by strong acids. Reaction mechanisms are proposed for both Substitutions. The Cl_3-nF_nCS group in aromatics exerts a -M-effect in the case of an attack of a positive ion, e.g. H^⊕, the well-known +M-effect in the case of reactions with positively polarized molecules, e.g. CF₃S^β+Cl^β-.     

Etude par diffraction de neutrons de la phase Sr0,5La1,5Li0,5Fe0,5O4

A neutron diffraction study has been carried out on Sr_0.5La_1.5Li_0.5Fe_0.5O₄ of K₂NiF₄-type derived structure and it has shown that iron in the tetravalent state has a high spin configuration (t³_2ge¹_g) and that the material has some stacking defects. At room temperature this compound shows an ordering between iron and lithium atoms leading to a nuclear cell a₀√2, a₀√2, c₀ (a₀ and c₀ are the parameters of the K₂NiF₄-type cell). At low temperature ($\text{T <}\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}$) the magnetic structure can be described as antiferromagnetic, corresponding likely to a colinear pattern with a propagation vector of 0.5 ($\text{2π}\text{a}{}_0$) along the [110] axis. At higher temperature ($\text{T}{}_{\mathrm{<mtext>N</mtext>}}\text{2}\text{< T < T}{}_{\mathrm{<mtext>N</mtext>}}$) helimagnetic structure is consistent with a propagation vector of 0.47 ($\text{2π}\text{a}{}_0$) [110].     

o-quinone methides 2. Stereoselectivity in cycloaddition reactions of o-quinone methides with vinyl ethers

Cycloaddition reactions between vinyl ethers 3 and $\text{o}$-quinone methides 2, thermally generated from 2-hydroxybenzyl alcohols 1, have been studied. The structure and conformational preferences of the 4-substituted 2-ethoxy-(2,3)-dihydro-2$\text{H}$-benzopyrans 4–9 obtained, which show new interesting features, are discussed together with competitive kinetic data. The cycloaddition process is concerted and involves $\text{o}$-quinone methides in the $\text{E}$-configuration. The OEt-$\text{endo}$ transition state seems to be preferred with ethyl vinyl ether and $\text{Z}$-1-propenyl ethyl ether, whereas with $\text{E}$-1-propenyl ethyl ether the stereoselectivity of the cycloaddition process depends on substituents on the methylene group of the starting alcohol 1. These results are discussed in terms of $\text{endo}$ and $\text{exo}$ preference of the propenyl ether methyl group.