3-methylthio-1,2-dithiolylium salts : Reaction with 4-hydroxy-6-methyl-2H-pyran-2-one and 4-hydroxycoumarin

The reaction of 4- and 5-aryl-3-methylthio-1,2-dithiolylium iodides with 4-hydroxy-6-methyl-2$\text{H}$-pyran-2-one and 4-hydroxycoumarin has been studied. 4-Substituted salts yielded 3-aryl-7-methyl-2-thioxo-2$\text{H}$,5$\text{H}$-pyrano [3,2-c]pyran-5-ones and 3-aryl-2-thioxo-2H,5H-pyrano[3,2-c]benzo[e]pyran-5-ones, respectively, whereas 5-substituted salts gave rise to 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-6-methyl-2$\text{H}$-pyran-2,4-diones and 3-(5′-aryl-1′,2′-dithiol-3′-ylidene)-2$\text{H}$-benzo [b]-pyran-2,4-diones.     

The chemical oxidation and electronic spectra of the complexes trans-[M(CNR)2(Ph2PCH2CH2PPh2)2] (M = Mo or W)

Oxidation of the complexes $\text{trans}$-[M(CNR)₂(dppe)₂] (A) (M = Mo or W; R = Me, Bu^t or CH₃C₆H₄-$\text{4}$; dppe = Ph₂PCH₂CH₂PPh₂) with diiodine or silver (I) salts gives the paramagnetic cations $\text{trans}$-[M(CNR)₂(dppe)₂]⁺, (M = Mo, R = CH₃C₆H₄-$\text{4}$; M = W, R = Bu^t) and $\text{trans}$-[M(CNR)₂(dppe)₂]²⁺ (M = Mo, R = Me or CH₃C₆H₄-$\text{4}$; M = W, R = Me or Bu^t). Mixtures of products are generally produced when dichlorine or dibromine are the oxidising agents, however pure salts, the seven-coordinate complex cations [MX(CNC₆H₄CH₃-$\text{4}$)₂(dppe)₂]⁺ (B, X = Cl or Br) have been isolated. A simple molecular orbital scheme is proposed for complexes (A) and used to discuss their electronic spectra and their oxidation.     

Studies on the biosynthesis of terrecyclic acid A II confirmation of the cyclization mechanism and hydrogen shifts using [2-2H3]acetate and [213C2H3]acetate

Feeding experiments with [2-³H₃]acetate and [2-¹³C²H₃]acetate in $\text{Aspergillus terreus}$ Thom No. 14 indicated that the hydrogen at C-2 in terrecyclic acid A is incorporated without migration from the precursor acetic acid; the results favour our group's earlier speculation for the cyclization to the tricyclic skeleton in the biosynthetic scheme.     

Biosynthesis of psilotin from [2′,3′-13C2,1′-14C,4-3H]phenylalanine studied with 13C-NMR

The 6-phenyl-dihydro-α-pyrone moiety of psilotin is formed from [2′,3′-¹³C₂,1′-¹⁴C,-4-³H]phenylalanine in the plant $\text{Psilotum}$$\text{nudum}$ with retention of all the isotopes.     

Oxidation of coordinated olefins: the reactions of Cl2 with trichloro(ehtylene)platinate(II)

The oxidation of [PtCl₃(C₂H₄)]- by Cl₂ in aqueous solution, to yield CH₂ClCH₂OH and [PtCl₄]^2-, has been shown to proceed through the following sequence of steps: [PtCl₃(C₂H₄)] Cl₂Cl [PtCl₅(CH₂CH₂Cl)]^2-$\text{H}{}_2\text{O}\text{(HCl)}$ [PtCl₅(CH₂CH₂OH)]^2- → [PtCl₄^2- + CH₂ClCH₂OHEach of the steps and intermediates in this mechanistic sequence has been identified and characterized.     

Boat-chair conformational preference of exo, exo-9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid

The ¹H and ¹³C nmr spectra of $\text{exo}$, $\text{exo}$-9-oxobicyclo[3.3.1]nonane-2,4-dicarboxylic acid, 3, in DMSO-d₆ or alkaline D₂O, clearly show that it exists in a $\text{boat}$-$\text{chair}$-conformation with $\text{equatorial}$ carboxyl groups, thus being the first case of $\text{boat}$-$\text{chair}$ preference of a bicyclo[3.3.1] nonan-9-one due to the presence of $\text{exo}$,$\text{exo}$-2,4- substituents.     

Biosynthesis of highly modified meroterpenoids in aspergillus variecolor. Incorporation of 13C-labelled acetates and methionine into anditomin and andilesin C

Incorporations of [1-¹³C]?, [2-¹³C]?, [1,2-¹³C₂]-acetates and [¹³C]-methionine into anditomin, a metabolite of $\text{Aspergillus variecolor}$, indicate its formation by a mixed polyketide-terpenoid biosynthetic pathway similar to that elucidated for andibenin; observations are made on the possible biosynthetic relationship of the $\text{A. variecolor}$ metabolites with austin and terretonin, mycotoxins recently isolated from $\text{A. ustus}$ and $\text{A. terreus}$ respectively.     

Biosynthesis of the Cytochalasans. Biosynthetic studies on chaetoglobosin A and 19-O-acetylchaetoglobosin A

Incorporation of [1-¹³C]-, [2-¹³C]- and [1,2-¹³C₂]-acetate, [1-¹³C]-propionate, [¹³C-CH₃]-L -methionine and [3-¹⁴C]-DL -tryptophan into chaetoglobosin A ( 1 ) and 19-O-acetylchaetoglobosin A ( 2 ) by Chaetomium globosum demonstrated that the building blocks of 1 and 2 are 9 and 10 units of acetate/malonate respectively, 3 units of methionine and 1 unit of tryptophan. Propionate is incorporated indirectly after several biological transformations. Using [2-¹³C, 2-²H₃]-acetate as precursor, the starter unit of the polyketide-chain was identified. Experiments which [¹³C, ²H₃-CH₃-L -methionine demonstrated that the three C-methylations occur with retention of all three H-atoms of the methyl group. Incorporation experiments with various ¹⁴C- and ³H-labelled tryphtophan samples and with [2-²H]- and [2-¹⁵N]-L -tryptophan showed that the amino acid is incorporated intact with retention of both the α-H- and the α-N-atom. On the basis of these results a more detailed general scheme of the cytochalasan biogenesis is proposed.     

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].     

Alkaline hydrolysis of 2-(trifluoromethyl)imidazo[4,5-f] and -[4,5-h]quinolines

2-(Trifluoromethyl)imidazo[4,5-$\text{f}$] and -[4,5-$\text{h}$]quinoline have been prepared from 5(6),acetamido-2-(trifluoromethyl)benzimidazole and 7,8-diaminoquinoline respectively. These (trifluoromethyl)- quinolines like 2-(trifluoromethyl)imidazoles but unlike 2-(trifluoromethyl) benzimidazoles, undergo hydrolysis in dilute sodium hydroxide to give ultimately the corresponding imidazo[4,5-$\text{f}$] and -[4,5-$\text{h}$]- quinoline, respectively.     

A kinetic study of the permanganate—oxalate reaction and kinetic determination of manganese(II) and oxalic acid by the stopped-flow technique

The reduction of permanganate by oxalate in the presence of manganese(II) ion in acidic media is described. All reactions were run at 525 nm and constant ionic strength 1.0 M. The reaction was found to obey the rate expression —$\text{d[MnO}{}_4{}^{\mathrm{-}}\text{]}\text{d}\text{t}$ = k [Mn²⁺] [C₂O₄^2-]² [MnO₄^-] [H⁺]^-2 = k' [MnC₂O₄] [MnO₄^-]. The values of k and k' were shown to be 5.4 × 10⁴ M^-1 s^-1 and 8.2 × 10⁴ M^-1 s^-1, respectively. Reaction rate methods for the determination of manganese(II) and oxalic acid are reported. The rate of disappearance of permanganate was monitored automatically and related directly to manganese-(II) and oxalic acid concentrations. Manganese(II) in the ranges 1–10 × 10^-4 M and 1–10 × 10^-3 M and oxalic acid in the range 0–20 μg ml^-1 can be determined very rapidly with a precision of 1–2%.     

Some reactions of 1,2,3,4,7,7-hexafluorobicyclo[2,2,1]hepta-2,5-diene: Thermolysis and attack by methoxide ion and by bistrifluoromethyl nitroxide

1,2,3,4,7,7-Hexafluorobicyclo[2,2,1]hepta-2,5-diene gave 1,2,3,4-tetrafluorebenzene in at least 73% yield when heated to 450°C in a sealed tube; the CF₂ bridge appeared, in part, as octafluorocyclobutane. Nucleophilic attack by sodium methoxide- methanol on the diene occurred exclusively at the CFCF bond, causing the formation of 1,2,4,7,7-pentafluoro-3-methoxybicyclo- [2,2,1]hepta-2,5-diene and a 1,4,5,6,7,7-hexafluoro-5-methoxybicyclo [2,2,1]hept-2-ene thought, on the basis of ¹⁹F nmr data, to be the 6-$\text{endo}$-F,5-$\text{exo}$-MeO isomer. Radical attack on 1,2,3,- 4,7,7-hexafluorobicyclo[2,2,1]hepta-2,5-diene by bistrifluoromethyl nitroxide took place at both olefinic sites, with a $\text{ca}$. 10:1 preference for the CFCF linkage; all three geometrical isomers of 5,6-bis(bistrifluoromethylamino-oxy)-1,4,5,6,7,7- hexafluorobicyclo[2,2,1]hept-2-ene were formed.     

Deuterium-induced 13C NMR isotope shifts for signal assignments and determination of deuteriation site in cyclododecanone

Deuterium-induced ¹³C isotope shifts were measured in the ¹³C {¹H} NMR spectra of monodeuteriated cyclododecanones formed upon oxidation of [1-²H₁] cyclododecanol with lead tetraacetate. These shifts, when used in conjunction with ¹³C NMR data of specifically labelled analogues, [2, 2, 12, 12-²H₄]- and [2-²H₁] cyclododecanone, enabled the ketone formed with lead tetraacetate to be identified as a mixture of [5-²H₁]- and [6-²H₁] isotopomers.     

Surface Mediated Organometallic Synthesis: Formation of [H5Os10(CO)24]− by Hydrogenation of Silica-Supported [Os(CO)3(OH)2]n as a Springboard for a High-Yield Synthesis of [H4Os10(CO)24]2− Starting from α-[Os(CO)3Cl2]2 and Working in Ethylene Glycol Solution

New high yield routes to the high nuclearity hydrido carbonyl clusters [H₅Os₁₀(CO)₂₄]^- and [H₄Os₁₀(CO)₂₄]^2-, model systems for the chemisorption of CO and H₂ on metal surfaces, are reported. [H₅Os₁₀(CO)₂₄]^- is obtained in good yields by hydrogenation (1 atm) at 200°C of physisorbed [Os(CO)₃(OH)₂]_n whereas in refluxing ethylene glycol solution, that is less acidic than the silica surface, [H₄Os₁₀(CO)₂₄]^2- is obtained in high yield starting from [Os(CO)₃(OH)₂]_n or, more conveniently, from -[Os(CO)₃Cl₂]₂ in the presence of the stoichiometric amount of sodium carbonate. The quantitative equilibrium

Functionalized 2-azabicyclo[3.3.1]nonanes. III.1 reductive rearrangement of an hexahydro-2-oxopyrano[3,2-b]pyridine

Reduction of 5-benzoyl-8-methyl-2-oxo-3,4,4a,5,6,7-hexahydro-2H-pyrano[3,2-b] pyridine ($\text{1}$) with lithium aluminium hydride afforded (1R^*,5S^*,6R^*,9S^*)-2-benzyl-5-methyl-2-azabicyclo[3.3.1]nonane-6,9-diol ($\text{2}$).     

X-ray molecular structure of the 1:1 adduct of [FeH(CO)4]− and dimethyl acetylenedicarboxylate. η3-[trans-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate

The crystal structure of a bis(triphenylphosphine)iminium salt of the 1:1 adduct of [FeH(CO)₄]^? and dimethyl acetylenecarboxylate has been determined from three-dimensional X-ray data collected by the counter method. Single crystals belong to the triclinic space space group P$\text{1}$, with two units of [C₃₆H₃₀NP₂]⁺[C₁₀H₇FeO₈]^? in a cell of dimensions: $\text{a}$ = 13.918(2), $\text{b}$ = 15.669(5), $\text{c}$ = 9.909(2) Å, $\text{α}$ = 91.22(3), $\text{β}$ = 94.83(2), and $\text{γ}$ = 77.62(2)°. The structure was refined to a conventional $\text{R}$ of 0.068 for 5373 observed

reflections. The resulting structure indicates that the complex anion is η³-[$\text{trans}$-2,3-bis(methoxycarbonyl)acryloyl]tricarbonylferrate, the coordination around the iron atom being described as a considerably distorted trigonal bipyramid. A comparison of the present structure with the structures of related complexes suggests that the η³-acryloyl portion is best represented as an intermediate of (η³-allyl) with the oxygen atom and (η²-olefin + η¹-acyl). The short Fe-C(acyl) length of 1.897(5) Å implies an enhanced back-donation of electrons from the iron atom to the acyl group.     

Platinum(0) complexes of 3-arylthiete 1,1-dioxides

3-Phenyl- and 3-p-bromophenyl-thiete 1,1-dioxides react with [Pt(trans-stilbene)(PPh₃)₂] and [Pt(AsPh₃)₄] to give the complexes [Pt($\text{CHCrCH}{}_2\text{S}$O₂)(MPh₃)₂] (R  Ph, p-BrC₆H₄; M P, As).     

Side-bonded ketone complexes of platinum(0). Alloxan and diethyl oxomalonate complexes and reactions of platinum(0) complexes with isatin and benzoyl cyanide.

Reactions of alloxan (all) with [PtL(PPh₃)₂] (L′= $\text{trans}$-stilbene, L″ diphenylacetylene) afford the side-bonded ketone complex [Pt(all)(PPh₃)₂] which may also be obtained from the hydrate of alloxan and [PtL′(Pph₃)₂]. Similarly diethyl oxomalonate (dio) and [Pt(PPh₃)₄] afford a side-bonded ketone complex [Pt(dio)(PPh₃)₂]. Reaction of isatin with [Pt(PPh₃₄] gives $\text{trans}$-[PtH{$\text{NCO(}\text{o}\text{-C}{}_6\text{H}{}_4\text{)CO}$}(PPh₃)₂] and benzoyl cyanide and [PtL′(PPh₃)₂] give $\text{cis}$-[Pt(CN)(COPh₃)₂] and $\text{trans}$-[Pt(CN)₂(PPh₂)₂].     

The reaction of trihydrobistriphenylphosphine iridium IrH3(PPh3)2 with diazonium salts

The reaction of IrH₃(PPh₃)₂ with p-substituted aryldiazonium salts gives the compounds [IrH₂(NHNC₆H₄R)(PPh₃)₂]⁺BF₄^- at low temperature (-10°C) and the o-metalated complexes [I$\text{rH(NHN}$C₆H₃R)(PPh₃)₂]⁺BF₄^- (R  F, OCH₃) at 40–50°C. The reactions of the o-metalated complexes with CO, PPh₃, NaI and HCl have been studied.     

Chiral [2H]-Labelled Methylene Groups in Trienoic- and Dienoic Fatty Acids: A Facile Approach via Asymmetric Epoxidation of [2H] Allyl Alcohols

Chiral [²H] -labelled methylene groups flanked by two double bonds within (poly)unsaturated fatty acids are readily available from trans-2,3-epoxy[2,3-²H₂] alk-4-yn-l-ols, obtained in their turn by asymmetric epoxidation of the corresponding (E)-[2,3-²H₂] alk-2-en-4-yn-l-ols (see Scheme 3). The procedure is exemplified for (8S,3Z,6Z,9Z)-[7,8-²H₂] trideca-3,6,9-trienoic acid ((8S)- 11 ) and (8R)- 11 (Scheme 4) as well as for (5S,3Z,6Z)-[4,5^?2H₂]deca-3,6-dienoic acid ((5S)- 13 ) and (5R)- 13 (Scheme 5).