Part I. Water-soluble organometallic catalysts for asymmetric reactions in aqueous media. Part II. Silylstannylative cyclization of unsaturated substrates catalyzed by palladium complex

A solution to the problem of separation of the catalyst from the product in homogeneous catalysis was developed using water-soluble catalysts derived from α,α′-trehalose and D-mannitol. Selective functionalization of α,α′-trehalose led to several macrocyclic phosphinite/phosphine ligands. The acid-labile protecting groups, i.e., cyclic ketal served best for the deprotection of Rh(I)-complexes of these organic-soluble ligands through the use of an acidic resin. The water-soluble Rh(I)-complexes thus formed are active hydrogenation catalysts for dehydroamino acids in water without any additives and the limitations thereof were discussed, such as lower enantioselectivities in water and hydrophobicity of the catalysts. These problems could be solved by use of hydroxyphospholanes synthesized from D-mannitol. The water-soluble ligand was generated by use of trifluoroacetic acid and resin-bound tertiary amine with tert-butyldimethylsilyl (TBS) ethers as protecting group. In catalyst recovery and reuse experiments, recycling of this catalyst was achieved up to 7th cycle. The enantioselectivities in the hydrogenation of dehydroamino acids remained at 99 %ee after 4th cycle without any loss of catalytic activity. Also, the availability of water-soluble free ligands is expected to lead to applications in homogeneous catalysis with metals other than rhodium.; Silylstannylative cyclization by palladium complexes was used for the cyclization of various unsaturated α,ω-bifunctional substrates with very high functional group compatibilities. The cyclization of diynes was applied to a synthesis of pyrrolizidine ring structure. A lack of regioselectivity was noted as a major limitation in the cyclization of unsymmetrical diynes. Among the potential schemes for solving the regioselectivity problem, the use of alleneyne as a substrate provided an attractive solution due to the higher reactivity of allene vs. acetylene. Various alleneynes could be efficiently cyclized in good yields to give carbo- and heterocyclic compounds with excellent regio- and stereocontrol. The use of allenes in the silylstannylative cyclization reaction was further applied in the synthesis of kainoid pyrrolidines to achieve synthesis of late intermediates of α-kainic acid.