Syntheses and mechanistic aspects of formation of 1,4-Diketopyrrolo[3,4-c]pyrroles (DPP) are discussed. The chemical reactivity of this novel class of heterocycles is illustrated by specific electrophilic aromatic and N-substitution reactions, as well as by nucleophilic transformations of the bicyclic lactam carbonyl group. X-ray structural analysis of the diphenyl-DPP molecule reveals significant intermolecular hydrogen bonding and IT-x interactions in the solid state.

ChemInform Abstract (lecture given at the XIIIth European Colloquium on Heterocyclic Chemistry, University of Fribourg, Switzerland, September 26-28, 1988).

SummaryThe photochemistry and some initiator characteristics of the polymerization initiators o, o-dimethoxy-w-phenyl-acetophenone (A), w, w-diethoxy-acetophenone (B) and o,w-diisopropoxy-acetophenone (C) have been studied by 'H-and '3C-chemically-induced nuclear polarization (CIDNP.) experiments. The primary reaction of initiator A is a Norrish-type I cleavage, while for B and C Norrish-type I and Norrish-type I1 cleavages are of comparable importance. Three different recombination products could be detected for initiator A which correspond to the three canonical resonance forms of the substituted benzyl radical.In a number of polymerization experiments the competition between reactions among initiator radicals and reactions of initiator radicals with the monomer acrylic acid methyl ester was studied at low concentrations of the monomer. These experiments give insight into the first steps of the polymerization process.The positive sign of the a-hydrogen hyperfine couplings of the dimethoxymethyl-and the diisoproproxymethyl-radicals could be established, in agreement with the deviation of these radicals from planarity.A slow square-wave light-modulation technique has been employed in 13C-FT.-experiments to measure absolute C1DNP.-intensities.

No abstract

Die Photochemie und die charakteristischen Eigenschaften der Polymerisationsinitiatoren wp‐Dimethoxy‐wphenyl‐acetophenon, cop‐Diethoxy‐ und o:,eo‐Diisopropoxy‐acetophenon wurden mit Hilfe 1H‐ und "C‐chemisch induzierter Kempolarisation untersucht.