All-forward semiclassical simulations of nonlinear response functions

We propose a quantum trajectory algorithm for computing nonlinear response functions of condensed phase molecular systems based on a time-ordered expansion of the density matrix. The nth-order response function is expressed as a sum of 2(n) impulsive response pathways representing trajectories involving zero, one, and up to n interactions with short external pulses. These are evaluated using a forward propagation algorithm based upon a Liouville space extension of the Bohmian propagation method.     

Characterizing individual scattering events by measuring the amplitude and phase of the electric field diffusing through a random medium

We describe observations of the amplitude and phase of an electric field diffusing through a three-dimensional random medium, using terahertz time-domain spectroscopy. These measurements are spatially resolved with a resolution smaller than the speckle spot size and temporally resolved with a resolution better than one optical cycle. By computing correlation functions between fields measured at different positions and with different temporal delays, it is possible to obtain information about individual scattering events experienced by the diffusing field. This represents a new method for characterizing a multiply scattered wave.     

Dynamic combinatorial libraries of metalloporphyrins: templated amplification of disulfide-linked oligomers

Disulfide-linked cyclic porphyrin oligomers from dimer to tetramer can be selected and amplified virtually quantitatively from a dynamic combinatorial library using bis-thiol substituted zinc(II) porphyrin units with appropriate amine donor templates.     

Lewis acid mediated cyclisations of silylated methylenecyclopropyl hydrazones

Silylated methylenecyclopropyl hydrazones on treatment with BF3 x Et2O cyclise to give heterocyclic products involving a novel sequence of hydride and silyl shifts via a series of increasingly stable cationic intermediates.     

The role of the counteranion in the cation-pi interaction

Chemical double mutant cycles have been used to quantify cation-pi interactions in chloroform as a function of the nature of the counteranion. The cation-pi interaction is -2.5 +/- 0.4 kJ mol(-1) and independent of the anion, even though the overall stability of the complexes varies by an order of magnitude due to competition of the anion for alternative binding sites.     

Rhodium-catalyzed enantioselective diboration of simple alkenes

Enantioselective catalytic reactions that operate directly on inexpensive unactivated alkenes are extraordinarily useful for the preparation of chiral organic building blocks and new materials. While a number of such processes have been developed, our ability to meet the intensifying demand for inexpensive stereochemically complex materials will require a significant expansion of practical catalytic asymmetric reaction methodology. In this regard, the rhodium-catalyzed enantioselective diboration reaction has been developed in order to address a number of extant problems in catalytic alkene transformation simultaneously. This process provides an enantiomerically enriched reactive dimetalated intermediate which can be converted to a variety of difunctional reaction products.     

Platinum-catalyzed tandem diboration/asymmetric allylboration: access to nonracemic functionalized 1,3-diols

[reaction: see text] A single-pot tandem catalytic diene diboration/carbonyl allylation reaction is described that uses a commercially available chiral diboron reagent. The chirality of the intermediate diboration adduct is transferred to the product in the carbonyl allylation reaction, thereby providing access to enantioenriched chiral products. Notably, the reaction allows for construction of a quaternary stereocenter and furnishes a synthetically versatile C-B bond in the reaction product.