α-Arylation and Ring Expansion of Annulated Cyclobutanones: Stereoselective Synthesis of Functionalized Tetralones

α-Arylcyclobutanones display unique reactivity that makes them valuable synthetic intermediates and target molecules. We describe the preparation of α-aryl- and α-heteroarylcyclobutanones through a direct α-arylation reaction. Problematic fragmentations are avoided by the use of LiO^tBu, which promotes a rapid but reversible self-aldol reaction that slowly releases the enolate required for α-arylation. We also demonstrate the ring expansion of α-arylcyclobutanones, a process that is highlighted in the stereoselective synthesis of 1-methoxy coniothyrinone D.     

Pendant arm pyrrolic amide cleft anion receptors

The propensity of amine, ammonium and amide pendant arm 2,5-diamidopyrrole derivatives to act as anion receptors has been investigated; the anion-coordination ability of these species has been determined by 1H NMR titration techniques revealing a marked selectivity of the amine functionalised receptor for hydrogen sulfate anions.     

Vibrational excitations and structure of C2H4 adsorbed on Cu(100)

The adsorption of C₂H₄ on Cu(100) at 80 K has been investigated by angle-dependent high-resolution electron energy loss spectroscopy (EELS) and low-energy electron diffraction (LEED). Our observations are consistent with a model where the ethene molecule is adsorbed in a configuration parallel to the Cu(100) surface. The molecule-metal interaction is weak and presumably of π character.     

An approach to developing a force field for molecular simulation of martensitic phase transitions between phases with subtle differences in energy and structure

d,l-Norleucine is one of only a few molecules whose crystals exhibit a martensitic or displacive-type phase transformation where the emerging phase shows a topotaxial relationship with the parent phase. The molecular mechanism for such phase transformations, particularly in molecular crystals, is not well understood. Crystalline phases that exhibit displacive phase transitions tend to be very similar in structure and energy. Consequently, the development of a force field for such phases is challenging as the phase behavior is determined by subtle differences in their lattice energies and entropies. We report an approach for developing a force field for such phases with an application to d,l-norleucine. The proposed procedure includes calculation of the phase diagram of the crystalline phases as a function of temperature to identify the best force field. d,l-Norleucine also presents an additional problem since in the solid state it exists as a zwitterion that is unstable in vacuo and therefore cannot be characterized using high-level ab initio calculations in the gas phase. However, a stable zwitterion could be obtained using Onsager's reaction-field continuum model for a solvent (SCRF) using both Hartree-Fock and density functional theory. A number of force fields and the various sets of partial charges obtained from the SCRF calculations were screened for their ability to reproduce the crystal structures of the two known phases, alpha and beta, of d,l-norleucine. Selected parameter sets were then employed in free energy minimizations to identify the best set on the basis of a correct prediction of the alpha-beta phase transition. The Williams' nonbonded parameters combined with partial charges from SCRF-Polarized Continuum Model calculation were found to reproduce the structures of the phases accurately and also maintained their stability in extended molecular dynamics simulations in the Parrinello-Rahman constant stress ensemble. Moreover, we were also able to successfully simulate the phase transformation of the beta- to the alpha-phase. The identified force field should enable detailed studies of the phase transformations exhibited by crystals of d,l-norleucine and hence enhance our understanding of martensitic-type transformations in molecular crystals.     

Honeycombs, herringbones and brick-walls; three-fold guest-dependent variation in copper trimesate complexes bearing sulfimide ligands

Reaction of a solution of CuSO(4) and S,S'-diphenylsulfimide, Ph(2)SNH 1, with sodium salts of trimesic acid (H(3)tma) in MeOH gives the 2-D coordination network [Cu(3)(Ph(2)SNH)(6)(tma)(2)] in which each trimesate is bound to three copper centres. Addition of other solvents to the reaction mixture causes a change in the shape of the network. By this route, three forms have been prepared and characterised by X-ray crystallography. These include the known honeycomb, 2, and brick-wall, 3, motifs and a herringbone, 4, arrangement which is novel for transition metal-containing trimesate complexes. Key to the supramolecular isomerism observed is the ability of 1 to facilitate structural isomerism at copper(II) centres. In contrast to 2 in which the copper centres are square planar, 4 is analogous to an inter-allogon, with both planar and tetrahedral copper centres. Also prepared is a related complex which is composed of discrete units of three copper centres. These are further linked into a 2-D network by hydrogen bonds.     

Nitrophenyl derivatives of pyrrole 2,5-diamides: structural behaviour,anion binding and colour change signalled deprotonation

Two new pyrrole 2,5-diamide clefts have been synthesized containing 4-nitrophenyl or 3,5-dinitrophenyl groups appended to the amide positions. The 3,5-dinitrophenyl derivative has been shown to deprotonate in the presence of fluoride, which in acetonitrile solution, gives rise to a deep blue colour.