A stereocontrolled partial synthesis of 1α-hydroxy vitamin D3

A novel and efficient partial synthesis of 1α-hydroxy vitamin D₃ ($\text{6}$), starting from 7-dehydrocholesterol ($\text{1}$), is reported. The crucial step in the synthesis involves a selective Diels-Alder reaction of 4-phenyl-1,2,4-triazoline-3,5-dione with the 6,8-diene system of previtamin D₃ ($\text{3}$), generating an adduct $\text{7}$ suitable for the stereoselective introduction of the 1α-hydroxyl group. Cycloreversion of $\text{13}$ leads to the title compound.     

A stereoselective synthesis of dl-3-epiuleine

A stereoselective synthesis of an indole alkaloid, 3-epiuleine, in racemic form is described. The key step involved is the ethylation of readily accessible compound $\text{5}$ with Et₂CuLi.     

A short and stereoselective synthesis of the (±) Prelog-Djerassi lactonic acid

Reaction of meso-4-carbomethoxy-2-methylpentanal ($\text{1}$) with crotyltri-n-butyltin at ?78°C in the presence of 1 eq BF₃·OEt₂, followed by the lactonization with BF₃·OEt₂, gave 6-(1-methylallyl)-3,4,5,6-tetrahydro-3,5-dimethyl-2-pyranone ($\text{2a}$) with the correct stereochemistry (erythro, anti-Cram) in 92% yield, which was converted to the title compound ($\text{3}$) in 85% yield upon the ozonolytic cleavage of the double bond.     

Reactions of triphenylarsine oxide with aqueous hydrogen fluoride: Crystal structure of bis(triphenylarsine oxide)hydrogen(I) tetrafluoroborate

Fluorination of triphenylarsine oxide by aqueous hydrogen fluoride (1–40%) in the absence of glass readily gives triphenylarsine difluoride. When the reaction with dilute (1%) aqueous hydrogen fluoride is carried out in borosilicate glass apparatus, the glass participates in the reaction resulting in the formation of the crystalline 2:1 adduct 2Ph₃AsO·HBF₄. Crystals of this compound are monoclinic, $\text{P}$2₁/$\text{c}$, $\text{a}$ = 12.926(4), $\text{b}$ = 17.819(6), $\text{c}$ = 14.994(4) Å, β = 98.97(3)°, Z = 4. The structure contains cations [(Ph₃AsO)₂H]⁺ in which $\text{O}\text{?}$O is 2.44(2)Å, and anions BF₄^?.     

Reaction of acylaminocyanoesters with 2,4-bis (4-methoxyphenyl)-1,3,2,4-dithiadiphosphetane 2,4-disulfide leading to substituted aminothiazoles. Crysta

2-Acylamino-2-cyanoacetic acid ethyl esters $\text{2a-c}$ react with 2,4-bis (4-methoxyphenyl)-1, 3, 2, 4-dithiadiphosphetane 2,4-disulfide $\text{1}$ in refluxing benzene with formation of 2-alkyl(aryl)-5-aminothiazole-4-carboxylic acid ethyl esters $\text{3a-c}$. Structure $\text{3}$ was established by spectroscopic means and an X ray crystallographic investigation of $\text{3a}$. X-Ray analysis revealed that the thiazole ring, exocyclic nitrogen and carbonyl group forming a hydrogen-bonded cycle are nearly coplanar. A resonance interaction is manifested by distinctly shortened /1.447 (3)/ C_(carbonyl)-C_(thiazole) distance.     

Bifurcarenone,an inhibitor of mitotic cell division from the brown alga bifurcaria galapagensis

A C₂₇ hydroquinone, bifurcarenone, apparently produced $\text{via}$ mixed biosynthesis, has been isolated from the brown seaweed $\text{Bifurcaria galapagensis}$ (Cystoseiraceae). The structure of bifurcarenone was determined by chemical and spectral methods, and this compound was found to exhibit antibacterial properties, as well as to inhibit cell cleavage of the fertilized egg from the urchin $\text{Strongylocentrotus purpuratus}$.     

The invention of new radical chain reactions. part X: High yield radical addition reactions of αβ-unsaturated nitroolefins. An expedient construction of the 25-hydroxy-vitamin D3 side chain from bi

Radicals derived from thiohydroxamic esters $\text{3}$ readily add to nitroolefins $\text{5}$ (Z = NO₂) to give good yields of α-nitrosulphides. These adducts, where the structure permits, are easily oxidised to carboxylic acids $\text{8}$ by treatment with alkaline hydrogen peroxide. Reductive cleavage to the corresponding aldehydes or ketones $\text{9}$ is efficiently carried out by the action of TiCl₃. Addition of methyl magnesium iodide to the methyl ketone derived from 3α-acetoxy 11-oxo cholanic acid gives steroid $\text{10}$ possessing the 25-hydroxycholesterol side chain of the vitamin D₃ metabotites. Radical additions to 1-phenylthio-2-nitropropene $\text{11}$ have been briefly studied.     

A novel deaminative cyclization of aminoglycoside. Synthesis of a kanamycin B variant having 2-oxa-5-azabicyclo[2,2,2]oct-1,5-diene ring

The 3′,5′-diene derivative of kanamycin B ($\text{2}$) was obtained from a 4′-ene derivative of kanamycin B ($\text{1}$) by treatment with trimethyl orthoacetate. Formation of the title compound ($\text{4}$) from $\text{2}$ deaminative cyclization with sodium methoxide followed by treatment with trifluoroacetic acid was described.     

A single crystal study of eight-layer barium managanese oxide,BaMnO3

A single crystal study of hydrothermally prepared eight-layer BaMnO₃ has been carried out which confirms the (Zhdanov notation) 121121 layer stacking scheme for the BaO₃ layers. The MnO₆ octahedra share faces in strings of four, and these strings are connected to each other by corner sharing. The compound has an hexagonal unit cell of dimensions a = 5.667 ± 0.003 and c = 18.738 ± 0.009 Å, probable space group $\text{P6}{}_3\text{mmc}\text{, Z = 8}$. Its structure has been determined from 352 independent reflections, of which 242 were considered observed, collected manually by a counter technique and refined to a conventional R value of 0.079.     

Structure of laurycolactone A and B,new C18 - quassinoids from Eurycoma longifolia and revised structured of Eurycomalactone (X - ray analysis)

Laurycolactone A $\text{2}$ and B $\text{3}$ are new quassinoids with a C₁₈ basic skeleton isolated from the Vietnamese Simaroubaceae, Eurycoma longifolia Jack. The structure of Eurycomalactone, a C₁₉ quassinoid isolated previously from the same plant, has been revised and shown to be $\text{4}$. The structures have been established by spectral means and those of $\text{2}$ and $\text{4}$ confirmed by X-ray diffraction analysis.     

Structure models for β-MnGa2S4 as derived from electron diffraction and high-resolution electron microscopy

A study by high-resolution electron microscopy and electron diffraction on the tetrahedrally coordinated compound β-MnGa₂S₄ is reported. The structure-imaging technique enabled a new structure model to be proposed for the accommodation of deviations from stoichiometry in compounds of the type $\text{x}\text{MnS}\text{y}\text{Ga}{}_2\text{S}{}_3$. The model is based on the Ga₂S₃ structure wherein by the substitution of MnS layers chemical twin planes are formed. Depending on the spacing of the periodic twin planes a homologous series of compounds is expected and a number of members of this series was identified mainly by electron diffraction. In the β-MnGa₂S₄ compound, two structure modifications are observed mainly differing in the orientation of the twin planes (coherent or incoherent). This conclusion is substantiated by structure image calculations for the interpretation of the high-resolution results.     

Isolation of aspirochlorine (=antibiotic A30641) possessing a novel dithiodiketopiperazine structure from Aspergillus Flavus

A very unusual dithiokikeptopiperazine structure ($\text{1}$) has been assigned to aspiroclorine, C₉H₁₂N₂O₅S₂Cl, produced as a biologically active substance together with canadensolide by $\text{Aspergillus}$$\text{flavus}$, which has been found to be identical with the antibiotic A 30641 from $\text{A.}$$\text{tamarii}$.     

A practical synthesis of fluoromethyltriphenylphosphonium salts

A practical synthesis of [Ph₃$\text{P}\text{+}$CH₂F]BF₄^? is reported $\text{via}$ two routes, $\text{via}$ fluorination of [Ph₃$\text{P}\text{+}$CH₂OH]BF₄^? with DAST or $\text{via}$ hydrolysis of the phosphoranium salt, [Ph₃$\text{P}\text{+}$$\text{C}$F$\text{P}\text{+}$Ph₃]Br^?.     

Étude structurale de combinaisons sulfurées et séléniées du molybdène: I. Structure cristalline de Mo3Se4

The crystals of Mo₃Se₄, are rhombohedral, space group $\text{R}\text{3}$, with two formula units in a cell: a = 6 658 Å, α = 91.58°.The structure was solved by the heavy atom method and refined by a full-matrix least-squares program to R = 0.045 for 537 independent reflexions. The structure consists of selenium chains parallel to the three axes such as those of metallic selenium, with wide channels running in the three directions. A few channels are occupied by “Mo₆” clusters so that Mo₃Se₄ can be regarded as a metallic compound.     

1-methyl-(D3)-trishomocubane

The acid catalysed rearrangement of 8-methyl-pentacyclo(5.4.0.0^2,6.0^3,10.0^5,9)undecan-8-endo-o1 ($\text{8}$) to 3-methyl-(D₃)-trishomocuban-4-o1 ($\text{9}$) provided the key step to the synthesis of the title compound ($\text{11}$).     

Synthesis of the serine equivalent, (2R) and (2S)-amino-3-butenol derivatives. Synthetic approaches to the metal chelating poly-amino acid, “aspergillomarasmine A”

Chiral synthons, equivalent to the C₃ amino acid serine, were synthesized in both (2$\text{R}$) and (2$\text{S}$) form from $\text{D}$ or $\text{L}$-methionine respectively; Utilization of this synthon in the construction of metal chelating poly-amino acid aspergillomarasminea A skeleton is presented.     

Magnetic susceptibility of the one-dimensional conductor (H3O)1.6[Pt(C2O4)2]nH2O

The magnetic susceptibility of the dioxalatoplatinate acid (H₃O)_1.6[Pt(C₂O₄)₂]nH₂O, a mixed valency planar (MVP) compound with columnar structure and one-dimensional metallic conduction properties, has been measured in the temperature range 1.5–300°K. The observed paramagnetism, like in other MVP compounds, may be described by a linear $\text{1}\text{T}$ dependence with a break in the slope at a characteristic temperature. The Curie constants as well as the point of discontinuity have been found to depend on the crystal water content. The results are discussed in terms of different theoretical concepts.     

Avenic acid,a new amino acid possessing an iron chelating activity

A new amino acid derivative possessing an iron chelating activity was isolated from root washings of water cultured $\text{Avena sativa}$ under iron deficient conditions. The structure of this compound, avenic acid A has been determined as 2(S),3′(S),3″(S)-N-[3-(3-hydroxy-3-carboxypropylamino)-3-carboxypropyl]-homoserine (1) on the basis of chemical and spectroscopic evidence.     

Ruthenium(0) Catalyzed Isomerization of Allylbenzene. The Detection and Isolation of A Hydrido-η3-Allyl Intermediate

Allylbenzene is isomerized to $\text{cis}$- and $\text{trans}$-β-methylstyrene at 35–60°C in the presence of [(C₆H₅)₃P]₄Ru(π-CH₃CN)·CH₃CN. Two hydrido-η³-1-phenylallyl ruthenium complexes have been detected by proton nmr spectroscopy during the reaction and the predominant one of formula [(C₆H₅)₃P]₂RuH(η³-C₃H₄C₆H₅)(CH₃CN) has been isolated. The structure of this intermediate contains cis phosphines, mutually trans hydrido and acetonitrile ligands and the 1-phenylallyl ligand in a $\text{syn}$-configuration. A similar structure with an $\text{anti}$-configuration of the 1-phenylallyl ligand is suggested for the other detected intermediate. These complexes indicate that this isomerization is initiated by oxidative-addition of ruthenium(0) to an allylic C-H bond with the formation of distinct η³-allyl metal hydride species as has been proposed in a number of metal catalyzed olefin transformations.     

Acid-base reactions of 1,3,4-thiadiazolines and thiocarbonyl ylides; 1,3,4-thiadiazoline-2-spiro-2′-adamantane

The surprising formation of C₂₂H₃₂N₂S₂ from the title compound 1 at 45°C involves the interaction of the basic adamantanethione S-methylide ($\text{2}$) with its acidic precursor $\text{1}$, in the course of which the anion $\text{6}$ undergoes electrocyclic ring opening; the acid and base functions offer the clue to a prolific chemistry of the thiadiazoline $\text{1}$ and the thiocarbonyl ylide $\text{2}$.