Formation of Titanium-Metallacycles and Exploration of Their Reactivities

1.(E)-烯丙醇是由(Z)-烯基砜与羰基化合物在二茂钛促进下通过氧杂环戊烷反应合成的。(Z)-烯基砜与炔烃的类似反应是通过生成钛环戊烯来立体选择性地生成共轭双烯。当使用乙酰羧酸衍生物和芳基膦酸酯时，还可以得到二烯羧酸、二烯羧酸酯和二烯基膦酸酯。(Z)-烯基砜-茂钛(II)体系与炔基砜的烷基化反应，生成的α-磺酰基烯基钛化合物的还原钛化反应生成了钛-乙烯基亚甲基络合物，该络合物在与羰基化合物的反应中具有完全的E-选择性。合成了不同取代方式的钛环丁烯，考察了它们对酮和端烯的反应活性。发现…中存在钛环丁烯。钛-烯基卡宾络合物的平衡程度较高，平衡的位置取决于其取代方式。1，1-二氯环丙烷与二茂钛试剂还原钛化生成的钛-环丙叉络合物与包括羧酸衍生物在内的羰基化合物反应，得到Wittig型烯化产物亚烷基环丙烷。通过多硫缩醛的脱硫钛化反应，还制备了多种多卡宾络合物，具有多种钛-卡宾络合物亚结构的有机钛物种。这些物种与羰基化合物反应生成各种高度共轭的化合物。钛-亚烷基络合物与炔基砜反应生成的钛环丁烯通过β消除生成了烯基钛物种。用酮处理这些有机钛物种，得到具有高非对映选择性的合叔丙基醇。相比之下，钛-环丙叉配合物与炔烃反应生成的螺环键合环丙烷的钛环丁烯是热稳定性的，可以分离出来。本研究阐明了四元钛环和五元钛环的反应性与结构的关系，从而开辟了有机钛化学的一个新领域。较少

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