dithiophenyl}, were prepared by treating TiCl 4 with the dilithium salts generated by reaction of the corresponding ligands (3, 4, 7, 8, and 11-15) with n BuLi in the presence of Et 3 N in toluene. In the ligand synthesis, the use of, respectively. X-ray crystallographic studies of 6, 17, and 19 indicate that the cyclopentadienyl moiety of 6 with TFCp (TFCp = thiophene-fused cyclopentadienyl) is bound to the titanium atom in an η 5 -fashion, whereas the coordination of the moieties to the metal in 17 and 19 with DTFCp (DTFCp = dithiophene-fused cyclopentadienyl) contributes in somewhat of an η 3 -manner. The newly prepared complexes 5, 6, 9, 10, and 16-20 exhibited high catalytic activities for copolymerization of ethylene and 1-hexene in the presence of i Bu 3 Al/[Me 2 NHPh][B(C 6 F 5 ) 4 ] and afforded higher molecular weight copolymer than the parent tetramethyl-substituted cyclopentadienyl complex Me 2 Si(η 5 -C 5 Me 4 )(3-t Bu-5-Me-2-C 6 H 2 O)TiCl 2 (1a). The complexes 6, 17, and 19 were thermally stable and exhibited high polymerization activities, even at 180 °C. Among tested complexes, the DTFCp complexes 17 and 19 at 180 °C showed very high activity and produced high molecular weight copolymers with good 1-hexene content.
The First Total Synthesis of Natural (-)-Tetracycline.-The key steps in the stereoselective synthesis of the title compound (XIV) involves the tandem Michael-Dieckmann type reaction of the chiral intermediate (VI) with the cyclic ester (VII) and the Diels-Alder reaction of the cyclohexenone (IV) and the silyloxybutadiene (V) leading to (VI). The transformation to the nitrile (XI) is a newly developed method. -(TATSUTA, KUNIAKI; YOSHIMOTO,
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.