Two New Modes of Pd-Catalyzed Domino-Tetracyclization of Bromodienynes—5-exo-trig Cyclization Wins over β-Hydride Elimination

Remarkable increases of molecular complexity in a single procedural step are achieved with the title reaction. Only a slight modification in the substitution pattern on the acyclic precursor 2 can change the mode of tetracyclization to either yield skeletons of type 1 or 3 exclusively.     

Crystal Structures – A Manifesto for the Superiority of the Valine‐Derived 5,5‐Diphenyloxazolidinone as an Auxiliary in Enantioselective Organic Synthesis

The crystal structures of 32 derivatives of 4‐isopropyl‐5,5‐diphenyl‐1,3‐oxazolidin‐2‐one ( A and 1 – 31 ) are presented (Fig. 2 and Tables 1–3). In all but four structures, the Me₂CH group is in a disposition that mimick a Me₃C group (Figs. 3–5). The five‐membered ring shows conformations from an envelope form with the Ph₂C group out of the plane containing the other four atoms to the twist form with the twofold axis through the CO group (Fig. 6, and Table 2). In the entire series, the Me₂CH and the neighboring trans Ph group are approximately antiperiplanar (average torsion angle 155°). The structural features are used to interpret the previously observed reactivity behavior of the diphenyl‐oxazolidinone derivatives. The practical advantages of the title compound over classical Evans auxiliaries are outlined (Figs. 1 and 7, and Scheme 2): high crystallinity of all derivatives, steric protection of the CO group in the ring, excellent stereoselectivities in reactions of its derivatives, and safe preparation and easy recovery of the auxiliary.     

A small-core multiconfiguration Dirac–Hartree–Fock-adjusted pseudopotential for Tl – application to TlX (X = F, Cl, Br, I)

 A relativistic pseudopotential of the energy-consistent variety simulating the Tl²¹⁺ (1s– 4f) core has been generated by adjustment to multiconfiguration Dirac–Hartree–Fock data based on the Dirac–Coulomb–Breit Hamiltonian. Valence ab initio calculations using this pseudopotential have been performed for atomic excitation energies and for spectroscopic constants of the X0⁺ and A0⁺ states of TlX (X = F, Cl, Br, I). Comparison is made to experiment and to four-component density functional results. Received: 22 June 1999 / Accepted: 5 August 1999 / Published online: 15 December 1999     

Letters to the Editor

The mathematical intelligencer encourages comments about the material in this issue. letters to the editor should be sent to either of the editors-in-chief, chandler davis or Marjorie Senechal.     

Analysis of metamaterials using transmission line models

We use simple transmission line models with lumped elements of inductance and capacitance to interpret optical transmission and reflection spectra of cut wires and cut-wire pairs in the near infrared region. The numerical values of the elements are obtained by fitting experimental or numerical simulated reflectance and transmittance spectra. The scattering parameters and the retrieved effective material parameters calculated from the transmission line models show good agreements with those obtained from experiments or numerical simulations. This indicates that transmission line theory is a powerful tool for designing and analyzing metamaterials at optical frequencies. PACS 41.20.Jb; 78.67.-n; 78.66.Sg