Studies on the synthesis of new ansa-metallocene

Abstract

The development of catalytic processes that effect enantioselective bond formation under mild conditions is an important and challenging task in modern chemical synthesis. In this connection, chiral $C_2$-symmetric ansa-metallocenes have found notable applications as catalysts. In order to study the effects of heteroatoms on the ring, new ansa-metallocenes were designed. From 4-pentynol, bis(enynes) 8 was synthesized. This bis(enynes) was also prepared from propargyl alcohol with low overall yield. This bis(enynes) was subject to Pauson-Khand reaction to give bis(cyclopentanone) 15. The other plan to synthesize new ansa-metallocene was to introduce stereocenters on the bridge. Synthesis from dimethyl-L-tartrate to bis(enynes) 17 and a plan that utilize Ti-based enantioselective homocoupling reaction as a key step were studied. From D-mannitol, bis(enynes) 47, 48, 50 were prepared effectively. These bis(enynes) were subjected to Pauson-Khand reaction in the hope to produce bis(cyclopetenones) only to yield cobalt coordinated complexes.