Palladium-katalysierte enantioselektive Umlagerung allylischer O-Thiocarbamate
Enantioselective Rearrangement of Allylic Thiocarbamates The aim of the project was the examination of Palladium(0) catalyzed rearrangements of allylic thiocarbamates. Influences of the allylic moity ant the substituents at the nitrogen were investigated in respect to reactiontimes, enantio-meric excesses of the products and used amounts of catalyst. Starting from racemic allylic alkohols the O-thiocarbmates were synthesized with alkyl isothiocyanates. As chiral ligand a bisphosphane ligand was used. With this ligand and Pd2(dba)3·CHCl3 as precatalyst the rearrangement of acyclic as cyclic thiocarbamates was achieved at roomtemperature with complete conversion. The products of this reaction were obtained with very good enantioselectivities (ee = 64->_99%) and yields (76-96%). Synthesis of Allylic Sufides from S-thiocarbamates It is possible to convert enantiomerically enriched allylic S-thiocarbamates to sufides. Under basic conditions acyclic as cyclic S-thiocarbamates could be substituted with chloropyrimidine to the corresponding pyrimidyle sulfide. Furthermore acyclic as cyclic allylic phenyl sulfides could be synthesized by a reaction under Heck conditions in presence of palladium acatate. In a aqueous solution of NaOH the cyclic thiocarbamates could be cleaved to the corresponding allylic thiols. Palladium-catalyzed Rearrangement of Allylic Thiocarbamates on Solid Support Starting from a polystyrene resin the rearrangement with the cyclohexene darrivative could be carried on solid phase. First the substrate was coupled to the resin under basic conditions. Adding the chiral bisphosphane ligand and Pd2(dba)3·CHCl3 caused the asymmetric rearrangement. Cleaving the S-thiocarbamate from the resin was achieved by transformation to allylic sulfides. Successfully carried out were the substitution with pyrimidyle chloride under basic conditions and the transformation to the phenyl sulfide under Heck-conditions. The enantioselectivity of this reaction, however, was lower than analogous reactions in solution.
info:eu-repo/classification/ddc/540, Chemie, Thiocarbamate, Allylgruppe, Umlagerung, Substituenteneffekt, Palladiumkomplexe, Katalysator
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