Studies On Rhodium-Catalyzed Asymmetric Cyclization Reactions Of 1, 6-Enynes

The transition metal-catalyzed carbocyclizations of 1,6-enynes are efficient and atom-economic methods to construct 5- or 6-membered ring frameworks, which widely exist in nature products and biologically active molecules. Recently, the asymmetric versions of some of these carbocyclizations have been achieved. However, the catalysts used in these asymmetric reactions are mainly limited to the metal complexes contained chiral atropoisomeric diphosphine ligands such as BINAP and BIPHEMP, and the enantioselectivities and substrate scopes of many of these reactions are far from beening satisfied. Thus, the development of efficient ligands catalysts for asymmetric carbocyclizations of 1,6-enynes remain to be a challenge for organic chemists. In this thesis we investigated the application of the chiral spiro phosphorus ligands in the rhodium catalyzed asymmetric carbocyclizations of 1,6-enynes.In the study of Rh(I)-catalyzed asymmetric Pauson-Khand reaction, we found that chiral spiro diphosphine ligand SDP was efficient. Under the optimized reaction conditions, the Rh(I)-SDP complex could convert a variety of 1,6-enynes to bicyclopentenone derivatives under CO atmosphere in high yields with good enantioselectivities. The ee values were up to 86% ee, which were comparable with those obtained by using BINAP type ligands.The monodentated chiral spiro ligands SIPHOS were also efficient for Rh-catalyzed Pauson-Khand reaction. By using SIPHOS-Rh(I) complex as catalyst, the cyclization products were produced in good yields and up to 84 % ee of enantioselectivities. This was the first example using monodentated phosphorus ligands to achieve a high enantioselectivity in the Rh(I)-catalyzed asymmetric Pauson-Khand reaction.In the Rh(I)-catalyzed asymmetric hydrosilylation/cyclization reaction of 1,6-enynes, chiral spiro diphosphine SDP ligands were demonstrated to be highly enantioselective. When the in situ generated catalyst from SDP and [Rh(COD)₂]BF₄ was used, a series of 1,6-enynes could react with silanes to provide the silylalkylidene cyclopentane or pyrrolidine derivatives in good yields with excellent enantioselectivties (up to 99.5% ee).This is the best result obtained in this reaction to date.Moreover, we had studied the Rh(I)-catalyzed asymmetric hydroformylation of vinyl arenes using monophosphorous Iigands. The spiro monophosphoramidite SIPHOS- 'Pr was the best ligand, providing the hydroformylation products in excellent yields (up to 99 %) with high regioselectivities (up to 97 %), and moderate enantioselectivities (up to 44 % ee).