Oxidation of alcohols by transition metal complexes—iv : The rhodium catalysed synthesis of esters from aldehydes and alcohols

Both RhH(CO)PPh₃)₃ and a catalyst made in _situ from RhCl₃·3H₂O, PPh₃ and Na₂CO₃ catalyse the reaction of a range of aldehydes with simple primary alcohols to give esters together with alcohols formed by reduction of the aldehydes. The proportion of ester can be increased by adding an efficient hydrogen acceptor. The reaction can also be used to produce 5- and 7-membered lactones from aromatic dialdehydes. Propan-2-ol and the _{in situ} catalyst reduce some aromatic aldehydes to the corresponding alcohols without concomitant ester formation.     

Unusual regiochemistry in a beckmann-like rearrangement of camphor. α-Camphidone via methylene migration.

Reaction of camphor with hydroxylamine-O-sulfonic acid affords the nitrogen insertion product α-camphidone by migration of the methylene group rather than the bridgehead. Since Beckmann rearrangements of trigonal oximes afford bridgehead cleavage products with camphor, an alternative synchronous rearrangement of a tetrahedral intermediate is proposed for this Beckmann-like reaction.     

Synthesis of methyl-1,6-dioxaspiro[4,5]decanes using organoselenium mediated cyclization reactions

Three naturally occurring methyl-1,6-dioxaspiro[4.5]decanes have been prepared in good yield using organoselenium mediated reactions during the crucial cyclization process.     

Translational energy disposal in molecular collisions: The transfer of momentum constraint

A Franck—Condon type argument, which requires the least transfer of momenta to the nuclei during a collision is outlined and applied to the analysis of translational energy disposal and its dependence on the initial translational energy. Using the maximal entropy procedure of information theory we are able to proceed directly from the assumed (model) constraint to the product state distribution.     

Novel annulene dications from methylated [2.2]metacyclophane monoenes and [e]-ring benzannelated dimethyldihydropyrene

Tetramethyl- and hexamethyl-substituted [2.2]metacyclophane monoenes (10 and 11) are transformed into their corresponding trans-dimethyldihydroethanophenanthrenium dications (14(2+) and 15(2+)) in FSO(3)H x SbF(5) (4:1) and FSO(3)H x SbF(5) (1:1) with SO(2)ClF or SO(2) as the solvent; these 10 pi-dications are equivalent to the C-4/C-5 diprotonated dications of the 2,7-dimethyl derivative of trans-DMDHP, 3a. The trans-12c,12d-dimethyl-12c,12d-dihydrobenzo[e]pyrene (6) reacts with FSO(3)H/SO(2)ClF under surprisingly mild conditions to give initially a persistent diprotonated dication (6H(2)(2+)) and, subsequently, the oxidation dication (6(2+)); the 6(2+):6H(2)(2+) ratio reaches 4:1 after 1 week at low temperature. Protonation of the anti-metacyclophane (13) was also examined. Charge delocalization mode and tropicity in the resulting dications are gauged via detailed NMR studies at 500 MHz.     

Modeling spatial patterns in Dictyostelium

The life cycle of Dictyostelium discoideum provides a striking example of the transition from single cell behavior to multicellular cooperativity. In this paper the status of the attempts at making semiquantitative models of the aggregation phase of this cycle is reviewed. Specifically, it is discussed how the propagation of cAMP waves is a typical example of excitable signaling, which is then rendered unstable by coupling to cell chemotaxis. To investigate the streaming pattern that emerges from this clumping instability, we next turn to a new simulation strategy, which couples dynamical cell-like entities ("bions") to continuum chemical concentration fields. Finally, we discuss two directions for further research: One is the study of the robustness with respect to the variation of system parameters (such as the cell density) exhibited by the biological system, but not by any simple model. The other concerns going beyond the aggregation phase to tackle the three-dimensional problem of slug formation and motion.     

Ergodicity of eigenfunctions for ergodic billiards

We give a simple proof of ergodicity of eigenfunctions of the Laplacian with Dirichlet boundary conditions on compact Riemannian manifolds with piecewise smooth boundaries and ergodic billiards. Examples include the Bunimovich stadium, the Sinai billiard and the generic polygonal billiard tables of Kerckhoff, Masur and Smillie.