The first total synthesis of the natural product (+)-K252a (2) has been achieved in 12 steps from commercially available materials, with a longest linear sequence of seven steps and an overall yield of 21%. The synthetic strategy employs novel rhodium carbenoid chemistry in the construction of both the indolocarbazole aglycon (4) and the carbohydrate moiety (9).

No abstract

An empirical model of the charge-density distribution in cyanuric acid, CaHaNaO3, was refined from X-ray data. The model consists of atomic cores and charge clouds that are placed at the bonds and in the lone-pair regions. The scattering factors for the atomic cores are derived by the L-shell projection method. The charge clouds are approximated by Gaussian distributions and, hence, their scattering factors are also Gaussian. The density parameters are defined in bond-oriented Cartesian coordinate systems, which allows the exploitation of the chemical (and not crystallographic) symmetry of the molecule as much as possible. Thus, the number of independent density parameters in the model was reduced to 36. The results of the refinement and of quantum-chemical calculations (4-31 G basis) are presented as dynamic and static difference densities, p(molecule) -p(isolated-atom model). The theoretical difference densities are in good agreement with experiment except for the p~ region of the N atoms. The theoretical bond peaks are lower than the experimental ones.

Record extinctions ε of 1.6×106 and 1.0×106 for the UV/Vis Soret bands, as well as extreme chemical shifts for the inner and outer perimeter protons in the 1H NMR spectra, characterize the two closely related 26π porphyrinoids 1 and 2, respectively. The dichotomy that 1 and 2 differ markedly in the extinctions of the Soret bands (appearing at nearly the same wavelength) yet almost agree—within the limits of comparison—in the 1H NMR spectra is explained convincingly on the basis of the molecular structures of the two compounds.