Formation of Titanium-Metallacycles and Exploration of Their Reactivities

1. (E)-烯基砜与羰基化合物经二茂钛（II）催化反应，以草酸环戊烷为原料制得烯丙基醇。(Z)-烯基砜与炔烃的类似反应是通过形成钛环戊烯生成立体选择性共轭二烯。当采用乙炔羧酸衍生物和乙烯基膦酸酯时，还可以得到二烯羧酸、二烯羧酸酯和二烯膦酸酯。炔基砜与(Z)-烯基砜-二茂钛（II）体系的烯基化反应以及α-磺基烯基钛化合物的还原钛化反应生成钛-乙烯基乙烯配合物，使烯基烯烯对羰基化合物具有完全的e选择性。合成了具有不同取代构型的环丁烯，并测定了它们对酮和端烯烃的反应性。结果表明，钛环丁烯与钛-烯基碳配合物的平衡位置取决于它们的取代模式。用二茂钛（II）试剂将1,1-二氯环丙烷还原钛化生成钛-环丙烯配合物，并与含羧酸衍生物的羰基化合物反应，得到了wittig型烯烃产物烷基烷基环丙烷。采用多硫缩醛的脱硫钛化法制备了多种多卡宾配合物，即具有多个钛-卡宾配合物亚结构的有机钛种。这些物质与羰基化合物反应生成各种高度共轭的化合物。烯基钛是由钛-烷基烯配合物与炔基砜反应生成的钛环丁烯进行β消除而得到的。用酮类处理这些有机钛得到具有高非对映选择性的同叔异丙基醇。而钛-环丙烯配合物与炔烃反应生成的含螺键环丙烷的钛环丁烯热稳定，可以分离得到。这些钛环水解生成烯基环丙烷。本研究阐明了四元和五元钛环反应性的结构依赖性，从而开辟了有机钛化学的一个新领域。少

1. (E)-Allylic alcohols were obtained via oxatitanacyclopentanes by the titanocene(II)-promoted reaction of (Z)-alkenyl sulfones with carbonyl compounds. The similar reactions of (Z)-alkenyl sulfones with alkynes proceeded via the formation of titanacyclopentenes to produce conjugated dienes stereoselectively. Dienecarboxylic acids, dienecarboxylic esters, and dienylphosphnic esters were also obtained when acetylenecarboxylic acid derivatives and alynylphosphonic esters were employed. The alkenylation of alkynyl sulfones with the (Z)-alkenyl sulfones-titanocene(II) system and the following reductive titanation of the resulting α-sulfonylalkenyltitaniurn compounds produced titanium-vinylvinylidene complexes which gave alkenylallenes with complete E-selectivity on treatment with carbonyl compounds.2. Titancyclobutenes with various substitution patterns were synthesized and their reactivity toward ketones and terminal alkenes was examined. It was found that titanacyclobutenes exist in equ … More ilibrium with titanium-alkenylcarbene complexes and the position of equilibrium depends on their substitution patterns.3. The Wittig-type olefination products, alkylidenecyclorpropanes, were obtained by the reaction of carbonyl compounds including carboxylic acid derivatives with titanium-cyclopropylidene complexes generated by the reductive titanation of 1,1-dichlorocyclopropanes with the titanocene(II) reagent. A variety of multicarbene complexes, organotitanium species having a plurality of titanium-carbene complex substructures, were also prepared by the desulfurizative titanation of multithioacetals. These species reacted with carbonyl compounds to produce various highly conjugated compounds.4. Allenyltitanium species were produced by the β-elimination of the titanacyclobutenes generated by the reaction of titanium-alkylidene complexes with alkynyl sulfones. The treatment of these organotitanium species with ketones gave syn-tertiary homopropargyl alcohols with high diastereoselectivity. In contrast, the titanacyclobutenes with a spiro-bonded cyclopropane generated by the reaction of titanium-cyclopropylidene complexes with alkynes were found to be thermally stable and could be isolated. The hydrolysis of these titanacycles produced alkenylcyclopropanes.The structure-dependence of reactivity of four- and five-membered titanacycles was elucidated by the present study, and thus a new field of organotitanium chemistry will be opened. Less