Stereo- and enantioselective synthesis using palladium, ruthenium and enzyme catalysis

Sammanfattning: In this thesis the use of palladium and ruthenium, with the latter in combination with enzymes, as selective catalysts in the transformation of organic substrates is discussed. The thesis is divided into two parts.The first part concerns the use of palladium(II) as a catalyst for the 1,4-oxidation of conjugated dienes using allylsilanes and carboxylic acids as internal nucleophiles. The reaction employing allylsilanes has been studied with two different reoxidation systems, p- benzoquinone and copper(II) chloride. By using the former oxidant highly stereoselective reactions took place, whereas the use of copper(II) chloride gave mixtures of isomeric products. It was demonstrated,by isolation and characterization of (p- allyl)palladium intermediates, that the allylsilane reacted as a nucleophile on the diene. The reactions using carboxylic acids as nucleophiles were conducted with the internal nucleophile connected to the side chain in the 2-position of the diene, giving six-membered lactones in good yields. High stereoselectivities across the diene were obtained, but in some cases the regioselectivity was lower and the 1,2-addition product wasformed.In the second part, studies of the combination of a ruthenium-catalyzed racemization with an enantioselective enzymatic acylation, in order to achieve a dynamic kinetic resolution ofsecondary alcohols, are described. It was found that the combination of a lipase from Candida antarctica, a stable ruthenium(II)-catalyst and a specifically designed acyl donor gave enantiomerically pure secondary acetates in good yields. Application of the reaction to symmetric diols gave enantiomerically pure diacetates in good yields and with high diastereoselectivities.