In examine the photocycloadditions of the title compounds the following questions are of interest: 1. Aside of [2+2]-cycloadditions to the C(2)=C(3) bonds, can any cycloaddition occur to the benzoid ring? 2. Which factors govern the regio- and stereoselectivity? Irradiation of either benzo[b]pyrrole-, -furane- or -thiophene-2-carboxylates in the presence of 2-morpholinopropennitril in cyclohexane leads, in a highly regioselective reaction, to [2+2] photoadducts. The regioselectivity seems to follow the formation of the most stable intermediate 1,4-biradicals. No photocycloadditions of the title alkene have been observed with 4-acceptor substituted benzo[b]pyrroles.

Algal alginates are of great importance for industrial applications. Since their properties depend on the kind of algae and the time of harvesting, supply problems caused price fluctuations. Hence, current research focuses on alternative alginate sources. Back in the 60s, exopolysaccharides similar to algal alginates were found. They were produced by mucoid Pseudomonas aeruginosa strains which embed themselves in a slime matrix containing bacterial alginates. The focus of this thesis was a comparisons of the physico-chemical properties of bacterial and algal alginates. The main results of the performed investigations are as follows: a) both substances aggregate in highly diluted solutions, b) bacterial alginates have a bigger molar mass than algal alginates, c) their mean squared radii of gyration are bigger than those of algal alginates, d) the second osmotic virial coefficients of these systems are negative and temperature dependent, e) acetylation of alginates support the aggregation, f) bacterial alginate do not gel analog to the egg box mechanism.

During the electronic excitation of 4-halo-1-acylnaphthalenes in the presence of a-cyanoenamines one could not only observe the typical cycloaddition, but also substitution of the halogen through C-3 of the cyanoenamine in a high degree. The photoreaction of halogenated 1-acetonaphthones as well as 1-methyl naphthoates with a-cyanoenamines resulted as a rule in two substitution products and regioselective in two "head/tail" 1,2-cycloadducts. One exception is 4-chloro-methyl-1-naphthoate with an additional "head/head"-adduct. The main product in all explored reactions is the E-substitutionproduct. The halogen substituent has an influences on the reaction pathway; 4-bromoacylnaphthalenes show much higher yields of substitutionproduct, which is due to the lower dissociation energy of the C-Br bond. As expected the halogenated methylketones show higher reactivity than the methyl ester. The methylketones prefer 1,2-Cycloadducts with donor-anti and the esters with donor-syn orientation. There is every reason to be ieve that the reaction mechanism for the formation of the substitution products is based on an electron transfer from the olefin to the triplet excited aromatic compound.

Two moderate electron-deficient propenoic acid derivatives have been investigated, with special emphasis on their reaction behaviour in cycloaddition reactions and comparison as to their capto-dative nature. In all reactions it was observed that the dehydroamino acid derivative resembles more an acrylic acid derivative than a capto-dative olefin. In reactions with various nitrones only 5,5'-disubstituted isoxazolidines were observed as products.