β‐Ionone reactions with the nitrate radical: Rate constant and gas‐phase products

The bimolecular rate constant of k (9.4 ± 2.4 × 10^?12 cm³ molecule^?1 s^?1 was measured using the relative rate technique for the reaction of the nitrate radical (NO₃?) with 4‐(2,6,6‐trimethyl‐1‐cyclohexen‐1‐yl)‐3‐buten‐2‐one (β‐ionone) at (297 ± 3) K and 1 atmosphere total pressure. In addition, the products of β‐ionone + NO₃? reaction were also investigated. The identified reaction products were glyoxal (HC(?O)C(?O)H), and methylglyoxal (CH₃C(?O)C(?O)H). Derivatizing agents O‐(2,3,4,5,6‐pentafluorobenzyl)hydroxylamine and N,O‐bis(trimethylsilyl)trifluoroacetamide were used to propose the other major reaction products: 3‐oxobutane‐1,2‐diyl nitrate, 2,6,6‐trimethylcyclohex‐1‐ene‐carbaldehyde, 2‐oxo‐1‐(2,6,6‐trimethylcyclohex‐1‐en‐1‐yl)ethyl nitrate, pentane‐2,4‐dione, 3‐oxo‐1‐(2,6,6‐trimethylcyclohex‐1‐en‐1‐yl)butane‐1,2‐diyl dinitrate, 3,3‐dimethylcyclohexane‐1,2‐dione, and 4‐oxopent‐2‐enal. The elucidation of these products was facilitated by mass spectrometry of the derivatized reaction products coupled with plausible β‐ionone + NO₃? reaction mechanisms based on previously published volatile organic compound + NO₃? gas‐phase mechanisms. The additional gas‐phase products 5‐acetyl‐2‐ethylidene‐3‐methylcyclopentyl nitrate, 1‐(1‐hydroxy‐7,7‐dimethyl‐2,3,4,5,6,7‐hexahydro‐1 H‐inden‐2‐yl)ethanone, 1‐(1‐hydroxy‐3a,7‐dimethyl‐2,3,3a,4,5,6,‐hexahydro‐1 H‐inden‐2‐yl)ethanone, and 5‐acetyl‐2‐ethylidene‐3‐methylcyclopentanone are proposed to be the result of cyclization through a reaction intermediate. © 2009 Wiley Periodicals, Inc. *

1 This article is a U.S. Government work and, as such, is in the public domain of the United States of America.

Int J Chem Kinet 41: 629–641, 2009     

Efficient templated synthesis of donor-acceptor rotaxanes using click chemistry

The mild reaction conditions, remarkable functional group compatibility, and complete regioselectivity of the Cu-catalyzed Huisgen 1,3-dipolar cycloaddition ("click chemistry") between organic azides and terminal alkynes have led to a threading-followed-by-stoppering approach to the synthesis of donor-acceptor rotaxanes incorporating cyclobis(paraquat-p-phenylene) (CBPQT4+) as the pi-accepting ring component. Rotaxane formation is initiated by reacting azide-functionalized pseudorotaxanes containing pi-donating 1,5-dioxynaphthalene (DNP) recognition units with appropriate alkyne-functionalized stoppers. The high yields obtained in this efficient, kinetically controlled post-assembly covalent modification, as well as the excellent convergence of the synthetic protocol, are demonstrated by the preparation of [2]-, [3]-, and [4]rotaxanes containing multiple DNP/CBPQT4+ donor-acceptor recognition motifs.     

Phosphonium-borate zwitterions, anionic phosphines, and dianionic phosphonium-dialkoxides via tetrahydrofuran ring-opening reactions

Sterically demanding secondary phosphines and phosphides react with (THF)B(C(6)F(5))(3) (THF = tetrahydrofuran) to give the THF ring-opened compounds [R(2)PHC(4)H(8)OB(C(6)F(5))(3)] and [Mes(2)PC(4)H(8)OB(C(6)F(5))(3)Li(THF)(2)] (Mes = C(6)H(2)Me-2,4,6). These reactions also occur consecutively to give the double THF ring-opened compounds [Mes(2)P(C(4)H(8)OB(C(6)F(5))(3))(2)][Li(THF)(4)] and [t-Bu(2)P(C(4)H(8)OB(C(6)F(5))(3))(2)Li].     

Alkyne coupling at a rhenium-monocarborane substrate: synthesis of Re,B-eta2:sigma-butadienyl complexes

Treatment of 7-NH(2)Bu(t)-nido-7-CB(10)H(12) in tetrahydrofuran (THF) with LiBu(n)(3 equiv) and then [ReBr(CO)(3)(THF)(2)] gives the rhenacarborane dianion [1-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)](2-), isolated as the bis-[N(PPh(3))(2)](+) salt (4). Iodine oxidation of this Re(I) intermediate gives the Re(III) complex [1,2-mu-NHBu(t)-2,2,2-(CO)(3)-closo-2,1-ReCB(10)H(10)] 6 in which the carborane functions formally as an 8-electron (6pi+ 2sigma) donor. Reaction of with ligands L in the presence of Me(3)NO gives substituted products [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-closo-2,1-ReCB(10)H(10)][L = PPh(3)(7a), CNXyl (7b; Xyl = C(6)H(3)Me(2)-2,6), or Bu(t)C triple bond CH (7c)]. Formation of complex 7c is unexpectedly accompanied by [1,2-mu-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)] 8a, in which an alkyne-derived dienyl group is bound to both the rhenium centre and to an adjacent boron vertex. Complex 8a is also obtained from 7c with Bu(t)C triple bond CH and Me(3)NO. The same reaction of 7c, using PhC triple bond CH or CNXyl instead of Bu(t)C triple bond CH, gives, respectively, [1,2-micro-NHBu(t)-2,2-(CO)(2)-3,2-sigma:eta(2)-{C(=CHBu(t))-CH=CHPh}-closo-2,1-ReCB(10)H(9)] 8b and [1,2-micro-NHBu(t)-2-Bu(t)C triple bond CH-2-CO-2-CNXyl-closo-2,1-ReCB(10)H(10)] 9. Addition of donors L to results in displacement from rhenium of the pendant dienyl moiety, yielding [1,2-mu-NHBu(t)-2,2-(CO)(2)-2-L-3-{C(=CHBu(t))-CH=CHBu(t)}-closo-2,1-ReCB(10)H(9)][L = PMe(3)(10a), CNBu(t)(10b)]. Single-crystal X-ray diffraction analyses have confirmed the novel structural features of compounds 6, 7c, 8b and 9.     

Water-soluble calix[4]resorcarenes as enantioselective NMR shift reagents for aromatic compounds

A tetra L-prolinylmethyl derivative of a tetra-sulfonated calix[4]resorcarene (1) is an effective chiral NMR solvating agent for water-soluble compounds with phenyl, pyridyl, bicyclic aromatic, or indole rings. These aromatic compounds form host-guest complexes with the calix[4]resorcarene in water. Complexation of substrates with the calix[4]resorcarene is likely promoted by hydrophobic effects, and bicyclic substrates have association constants with the calix[4]resorcarene larger than those of similar phenyl-containing compounds. Aromatic resonances of the substrates show substantial upfield shifts because of shielding from the aromatic rings of the calix[4]resorcarene, and several resonances in the 1H NMR spectra typically exhibit enantiomeric discrimination. The extent of enantiomeric discrimination depends in part on interactions of the substituent groups of the substrates with the prolinylmethyl groups of the calix[4]resorcarene. The effectiveness of a calix[4]resorcarene prepared from N-methyl-L-alanine (2) as a chiral NMR discriminating agent is compared to the L-prolinylmethyl derivative.     

Structure, energetics, and reactions of alkali tetramers

Electronic structure calculations have been carried out for all possible alkali tetramers that can be formed from X(2) + X(2) → X(2)X(2), X(2) + Y(2) → X(2)Y(2), and XY + XY → X(2)Y(2) alkali dimer association reactions. Vibrationally stable rhombic (D(2h)) and planar (C(s)) structures are found for all possible tetramers formed from the alkali metals, Li to Cs. All tetramer formation reactions (from ground state singlet homonuclear or heteronuclear dimers) are found to be exothermic with binding energies ranging from 6282 cm(-1) for Li(2)Li(2) to 1985 cm(-1) for Cs(2)Cs(2). Extensive calculations, carried out at long-range for several reactant pairs, indicate that there are barrier-less pathways for the formation of tetramers from dimer association reactions. At low temperatures, direct formation of tetramers is unlikely, owing to the large exothermicity associated with these association reactions, but atom exchange reactions (X(2) + Y(2) ? XY + XY) are possible for some species.     

Mixed-sequence pyrrolidine-amide oligonucleotide mimics: Boc(Z) synthesis and DNA/RNA binding properties

Pyrrolidine-amide oligonucleotide mimics (POMs) exhibit promising properties for potential applications, including in vivo DNA and RNA targeting, diagnostics and bioanalysis. Before POMs can be evaluated in these applications it is first necessary to synthesise and establish the properties of fully modified oligomers, with biologically relevant mixed sequences. Accordingly, Boc-Z-protected thyminyl, adeninyl and cytosinyl POM monomers were prepared and used in the first successful solid phase synthesis of a mixed sequence POM, Lys-TCACAACTT-NH2. UV thermal denaturation studies revealed that the POM oligomer is capable of hybridising with sequence selectivity to both complementary parallel and antiparallel RNA and DNA strands. Whilst the duplex melting temperatures (Tm) were higher than the corresponding duplexes formed with isosequential PNA, DNA and RNA oligomers the rates of association/dissociation of the mixed sequence POM with DNA/RNA targets were noticeably slower.