Regioselective synthesis of substituted pyrroles: efficient palladium-catalyzed cyclization of internal alkynes and 2-amino-3-iodoacrylate derivatives

The first efficient and regioselective palladium-catalyzed cyclization of internal alkynes and 2-amino-3-iodoacrylates to give moderate to excellent yields of highly functionalized pyrroles has been developed. This approach is applicable to a range of alkynes and affords the deacylated pyrrole under reaction conditions for most substrates. [reaction: see text]     

Generalized principal series representations of

We consider certain induced representations of the group
realized on line bundles over the projective space of . We calculate the intertwining operators in the compact picture. We find all the unitarizable representations and determine the invariant norm.

     

Synthesis of neutral spin-delocalized electron acceptors for multifunctional materials

A new synthetic route to stable spin-delocalized radicals, annelated nitronyl nitroxides, has been developed on the basis of the condensation of benzofuroxan with aryl nitrones. The electronic structure of the resulting radicals was investigated through absorption spectroscopy, EPR, electrochemistry, and computation (DFT-UB3LYP). The annelated radicals exhibit electronic transitions in the near IR (850-900 nm) and are excellent electron acceptors (E(red) approximately 0.0 vs SCE) ideal for the development of multifunctional magnetic materials.     

Enthalpies of formation, bond dissociation energies and reaction paths for the decomposition of model biofuels: ethyl propanoate and methyl butanoate

The complete basis set method CBS-QB3 has been used to study the thermochemistry and kinetics of the esters ethyl propanoate (EP) and methyl butanoate (MB) to evaluate initiation reactions and intermediate products from unimolecular decomposition reactions. Using isodesmic and isogeitonic equations and atomization energies, we have estimated chemically accurate enthalpies of formation and bond dissociation energies for the esters and species derived from them. In addition it is shown that controversial literature values may be resolved by adopting, for the acetate radical, CH3C(O)O(.-), DeltaH(o)(f)298.15K) = -197.8 kJ mol(-1) and for the trans-hydrocarboxyl radical, C(.-)(O)OH, -181.6 +/- 2.9 kJ mol(-1). For EP, the lowest energy decomposition path encounters an energy barrier of approximately 210 kJ mol(-1) (approximately 50 kcal mol(-1)), which proceeds through a six-membered ring transition state (retro-ene reaction) via transfer of the primary methyl H atom from the ethyl group to the carbonyl oxygen, while cleaving the carbon-ether oxygen to form ethene and propanoic acid. On the other hand, the lowest energy path for MB has a barrier of approximately 285 kJ mol(-1), producing ethene. Other routes leading to the formation of aldehydes, alcohols, ketene, and propene are also discussed. Most of these intramolecular hydrogen transfers have energy barriers lower than that needed for homolytic bond fission (the lowest of which is 353 kJ mol(-1) for the C(alpha)-C(beta) bond in MB). Propene formation is a much higher energy demanding process, 402 kJ mol(-1), and it should be competitive with some C-C, C-O, and C-H bond cleavage processes.     

Matrix coefficients and coadjoint orbits of compact Lie groups

Let be a compact Lie group. We use Weyl functional calculus (Anderson, 1969) and symplectic convexity theorems to determine the support and singular support of the operator-valued Fourier transform of the product of the -function and the pull-back of an arbitrary unitary irreducible representation of to the Lie algebra, strengthening and generalizing the results of Cazzaniga, 1992. We obtain as a consequence a new demonstration of the Kirillov correspondence for compact Lie groups.

     

Theory of sheath in a collisional multi-component plasma

The aim of this brief report is to study the behaviour of sheath structure in a multi-component plasma with dust-neutral collisions. The plasma consists of electrons, ions, micron size negatively charged dust particles and neutrals. The sheath-edge potential and sheath width are calculated for collisionally dominated sheath. Comparison of collisionless and collisionally dominated sheath are made.     

Continuous singular measures with absolutely continuous convolution squares

We prove for every non-abelian compact connected group there is a continuous, singular, central measure with in for all . We also construct such measures on some families of non-abelian compact totally disconnected groups. These results settle an open question of Ragozin.

     

3-pyrrolines are mechanism-based inactivators of the quinone-dependent amine oxidases but only substrates of the flavin-dependent amine oxidases

We previously reported that 3-pyrroline and 3-phenyl-3-pyrroline effect a time-dependent inactivation of the copper-containing quinone-dependent amine oxidase from bovine plasma (BPAO) (Lee et al. J. Am. Chem. Soc. 1996, 118, 7241-7242). Quinone cofactor model studies suggested a mechanism involving stoichiometric turnover to a stable pyrrolylated cofactor. Full details of the model studies are now reported along with data on the inhibition of BPAO by a family of 3-aryl-3-pyrrolines (aryl = substituted phenyl, 1-naphthyl, 2-naphthyl), with the 4-methoxy-3-nitrophenyl analogue being the most potent. At the same time, the parent 3-phenyl analogue is a pure substrate for the flavin-dependent mitochondrial monoamine oxidase B from bovine liver. Spectroscopic studies (including resonance Raman) on BPAO inactivated by the 4-methoxy-3-nitrophenyl analogue are consistent with covalent derivatization of the 2,4,5-trihydroxyphenylalanine quinone (TPQ) cofactor. The distinction of a class of compounds acting as an inactivator of one amine oxidase family and a pure substrate of another amine oxidase family represents a unique lead to the development of selective inhibitors of the mammalian copper-containing amine oxidases.     

Vibrational state-dependent predissociation dynamics of ClO (A (2)Pi(3/2)): Insight from correlated fine structure branching ratios

We have studied the v'-dependent predissociation dynamics of the ClO A (2)Pi(3/2) state using velocity-map ion-imaging. Experimental final correlated state branching ratios, i.e. Cl((2)P(J=3/2,1/2)) + O((3)P(J=2,1,0)) channels, have been measured for v' = 6-11. We find that the branching ratios are highly variable and depend strongly on v', providing a window into the v'-dependent predissociation mechanism. A comparison of the experimental results with the recent model of Lane et al. (I. C. Lane, W. H. Howie and A. J. Orr-Ewing, Phys. Chem. Chem. Phys., 1999, 1, 3087) in both the diabatic and adiabatic limits suggests that the dynamics are closer to the diabatic limit. The overall Cl((2)P(J)) branching ratios are in good agreement with the diabatic model results. There are significant differences, however, between theory and experiment at the correlated state level, demonstrating the sensitivity of correlated measurements to the role of the exit channel coupling in the predissociation dynamics. The results highlight the need for more sophisticated quantum dynamical calculations to describe the correlated fine structure branching ratios in this system.