Hydrocarbon oxidation vs C-C bond-forming approaches for efficient syntheses of oxygenated molecules

[Reaction: see text] A hydrocarbon oxidation approach has been applied to the construction of several linear (E)-allylic alcohols that have served as intermediates in the synthesis of natural products and natural product-like molecules. In the original syntheses, these intermediates were constructed using a standard Wittig-type olefination approach. We report here that routes to these same intermediates designed around a hydrocarbon oxidation approach are more efficient both in the total number of functional group manipulations (FGMs) and overall steps, as well as in the overall yield.     

Synthesis and NMR-Spectroscopic Structure Determination of Novel 7,7′-Diphenyl-7,7′-diapocarotenoids

Wittig reaction of crocetindial ( 1 ) and benzylidenetripenylphosphorane ( 2 ) gave (7E, 7′Z)-7,7′-diphenyl-7-7′-diapocarotene ( 3 ), instead of the previously reported (7E, 7′E)-isomer. Similar reaction of 8,9-didehydrocrocetindial ( 4 ) with 2 yielded the three acetylenic isomers 5a–c which differ in the configuration of the terminal double bonds. Structures were established by 1D- and 2D-NMR studies. Illustrative spectra and their interpretation are presented. Most chemical shifts of corresponding protons in 3 and 5 and nearly identical, but ¹³C shifts differ considerably.     

Determination of low-molecular-weight carboxylic acids in aqueous samples by gas chromatography and nitrogen-selective detection of 2-nitrophenylhydrazides

A gas chromatographic method was developed for the determination of low-molecular-weight carboxylic acids in aqueous samples based on a derivatization procedure compatible with aqueous solutions. The technique uses nitrogen-selective detection with a thermionic-specific detector after derivatization of carboxylic acids as 2- nitrophenylhydrazides. The hydrazides were extracted with ethyl acetate prior to injection into the gas chromatograph. The derivatives appear to be stable in ethyl acetate at 0–5° C for long periods and, therefore, can be stored for analysis at a later date. The detection limits of different short-chain acids are in the range 0.8–1.4 pmol per injected sample. The relative standard deviation is less than 10% at the 1 μM level. Examples of the use of the method are given for the determination of carboxylic acids in anoxic marine sediment pore waters, coastal sea water and Black Sea water samples.     

Hexadentate hydroxypyridonate iron chelators based on TREN-Me-3,2-HOPO: variation of cap size

TREN-Me-3,2-HOPO, TR322-Me-3,2-HOPO, TR332-Me-3,2-HOPO, and TRPN-Me-3,2-HOPO correspond to stepwise replacement of ethylene by propylene bridges. A series of tripodal, hexadentate hydroxypyridinone ligands are reported. These incorporate 1-methyl-3,2-hydroxypyridinone (Me-3,2-HOPO) bidentate chelating units for metal binding. They are varied by systematic enlargement of the capping scaffold which connects the binding units. The series of ligands and their iron complexes are reported. Single crystal X-ray structures are reported for the ferric complexes of all four tripodal ligands: FeTREN-Me-3,2-HOPO.0.375C(4)H(10)O.0.5CH(2)Cl(2) [P2(1)/n (No. 14), Z = 8, a = 20.478(3) A, b = 12.353(2) A, c = 27.360(3) A; beta = 91.60(1) degrees ]; FeTR322-Me-3,2-HOPO.CHCl(3).0.5C(6)H(14).CH(3)OH.0.5H(2)O [P2(1)/n (No. 14), Z = 4, a = 12.520(3) A, b = 22.577(5) A, c = 16.525(3) A; beta = 111.37(3) degrees ]; FeTR332-Me-3,2-HOPO.3.5CH(3)OH [C2/c (No. 15), Z = 8, a = 13.5294(3) A, b = 19.7831(4) A, c = 27.2439(4) A; beta = 101.15(3) degrees ]; FeTRPN-Me-3,2-HOPO.C(3)H(7)NO.2C(4)H(10)O [P1 (No. 2), Z = 2, a = 11.4891(2) A, b = 12.3583(2) A, c = 15.0473(2) A; alpha = 86.857(1) degrees, beta = 88.414(1) degrees, gamma = 70.124(1) degrees ]. The structures show the importance of intermolecular hydrogen bonds and the effect of cap enlargement to the stability and geometry of the metal complexes throughout the series. All protonation and iron complex formation constants have been determined from solution thermodynamic studies. The TREN-capped derivative is the most acidic, with a cumulative protonation constant, log beta(014), of 25.95. Corresponding values of 26.35, 26.93, and 27.53 were obtained for the TR322, TR332, and TRPN derivatives, respectively. The protonation constants and NMR spectroscopic data are interpreted as being due to the influence of specific hydrogen-bond interactions. The incremental enlargement of ligand size results in a decrease in iron-chelate stability, as reflected in the log beta(110) values of 26.8, 26.2, 26.42, and 24.48 for the TREN, TR322, TR332, and TRPN derivatives, respectively. The metal complex formation constants are also affected by the acidity of a proximal (non-metal-binding) amine in the complexes, a trend consistent with the effects of internal hydrogen bonding. The ferric complexes display reversible reduction potentials (measured relative to the normal hydrogen electrode (NHE)) between -0.170 and -0.223 V.     

Silver and palladium complexes of some aromatic azo and azoxy compounds

The complexing ability of derivatives of azobenzene (I) is well known (I) and responsible for the production of a wide variety of dyestuffs and analytical chemicals. While the azo group generally participates in the coordination, the determination of the degree of its interaction is complicated by other functional groups which are also coordinated with the transition metal. In a previous publication (2), we reported the preparation of the silver and palladium complexes of benzo[c]cinnoline (II) and proposed that these results might be used to explain the electron donor properties of azobenzene. We are now reporting the preparation of some additional complexes with ligands containing the azo group.     

Adhesive transfer of thin viscoelastic films

Micellar suspensions of acrylic diblock copolymers are excellent model materials for studying the adhesive transfer of viscoelastic solids. The micellar structure is maintained in films with a variety of thicknesses, giving films with a well-defined structure and viscoelastic character. Thin films were cast onto elastomeric silicone substrates from micellar suspensions in butanol, and the adhesive interactions between these coated elastomeric substrates and a rigid indenter were quantified. By controlling the adhesive properties of the film/indenter and film/substrate interfaces we were able to obtain very clean transfer of the film from the substrate to the portion of the glass indenter with which the film was in contact. Adhesive failure at the film/substrate interface occurs when the film/indenter interface is able to support an applied energy release rate that is sufficient to result in cavity nucleation at the film/substrate interface. Cavity formation is rapidly followed by delamination of the entire region under the indenter. The final stage in the transfer process involves the failure of the film that bridges the indenter and the elastomeric substrate. This film is remarkably robust and is extended to three times its original width prior to failure. Failure of this film occurs at the periphery of the indenter, giving a transferred film that conforms to the original contact area between the indenter and the coated substrate.     

A theoretical (DFT, GIAO-NMR, NICS) study of the carbocations and oxidation dications from azulenes, homoazulene, benzazulenes, benzohomoazulenes, and the isomeric azulenoazulenes

Protonation of parent azulene (1), homoazulene (8), representative isomeric benzazulenes (9, 9A, and 9B), and benzohomoazulenes (10, 10A, and 10B) as well as the mono- and diprotonation of isomeric azulenoazulenes (11-16) were studied by DFT at the B3LYP/6-31G(d) level. The most likely carbocations were identified based on relative protonation energies. For comparison, complete experimental 13C NMR data were obtained for parent azulenium ion 1H+ and guaiazulenium ion 2H+ in TFA. The oxidation dications derived from benzazulenes (9, 9A, and 9B), benzohomoazulenes (10, 10A, and 10B) and azulenoazulenes (11, 16) were also investigated. For azulenoazulene dications the singlet and triplet states are both minima, but except for 11(2+) and 13(2+), the triplet states are higher in energy. Structural/geometrical changes in the carbocations were examined. GIAO-NMR, NPA charges (and changes in charges), and NICS (and delta NICS) were employed to compute the NMR chemical shifts (delta delta 13C values) in order to derive charge delocalization maps and to gauge relative aromaticitylantiaromaticity in the energetically most favored carbocations and oxidation dications. The emerging trends are discussed and compared. Creation of tropylium or homotropylium entities in the carbocations (monoprotonated) and carbodications (diprotonated) is identified as an important driving force governing the protonation outcomes. Consideration of the AM1-derived delta delta Hf values (and the DFT-derived delta delta G values) suggests that the two-electron oxidation of azulenoazulenes should be experimentally feasible. Given their antiaromatic (paratropic) character, azulenoazulene dications represent interesting targets for NMR study. GIAO-derived charge delocalization mapping allows the most likely sites for nucleophilic attack on the dications to be identified.     

The synthesis of N-substituted ketimines from oxazirdines

N-Unsubstituted diaryl, alkyl aryl and dialkyl ketimines are prepared in good yield at ambient temperature by the reaction of KOBu^t on oxaziridines having an α-hydrogen atom on the N-alkyl substituent; the mechanism and stereochemistry of the reaction are discussed.     

Time-dependent pump-probe spectra of NeBr2

Time- and frequency-resolved pump-probe measurements on NeBr2 have been performed to better characterize its fragmentation dynamics on the B electronic state for vibrational levels in the energy region of the transition from direct vibrational predissociation to intramolecular vibrational relaxation dynamics. Above nu'=20 of the Br2 stretching mode, it was observed that the dependence of lifetime on the vibrational quantum number deviates from the energy-gap law by leveling off in the range of 10 psE transitions of the complex. These transitions are shifted 20 cm(-1) to lower energy from the free Br2 resonances, indicating an E state Ne-Br2 bond energy of 82 cm(-1). Measurements of NeBr2 vibrational predissociation via the delta nu=-2 channel were also performed for nu'=27, 28, and 29. The closing of the delta nu=-1 channel leads to an increase in the lifetimes of these vibrational levels. A new Nd:yttrium aluminum garnet pumped dual optical parametric oscillator/optical parametric amplifier system is described that allows us to conveniently record time-delayed pump-probe spectra with 2-cm(-1) spectral resolution and 15-ps time resolution.     

Aerobic oxidation of methyl p-tolyl sulfide catalyzed by a remarkably labile heteroscorpionate RuII-aqua complex,fac-[RuII(H2O)(dpp)(tppm)]2+

fac-[RuII(Cl)(dpp)(L3)]+ (L3 = tris(pyrid-2-yl)methoxymethane (tpmm) = [1A]+ and tris(pyrid-2-yl)pentoxymethane (tppm) = [1B]+ and dpp = di(pyrazol-1-yl)propane) rapidly undergo ligand substitution with water to form fac-[RuII(H2O)(dpp)(L3)]2+ (L3 = tpmm = [2A]2+ and tppm = [2B]2+). In the structure of [2A]2+, the distorted octahedral arrangement of ligands around Ru is evident by a long Ru(1)-O(40) of 2.172(3) A and a large angle O(40)-Ru(1)-N(51) of 96.95(14) degrees . The remarkably short distance between O(40) of H2O and H(45a) of dpp confirms the heteroscorpionate ligand effect of dpp on H2O. [2B]2+ aerobically catalyzes methyl p-tolyl sulfide to methyl p-tolyl sulfoxide in 1,2-dichlorobenzene at 25.0 +/- 0.1 degrees C under 11.4 psi of O2. Experimental facts in support of this aerobic sulfide oxidation are the absence of H2O2 and the oxidative reactivity of the putative Ru(IV)-oxo intermediate toward methyl p-tolyl sulfide, 2-propanol, and allyl alcohol. This study provides the first documented example of aerobic-sulfide oxidation catalyzed by the remarkably labile heteroscorpionate Ru(II)-aqua complex without the formation of a highly reactive peroxide as an intermediate.