Formation of Titanium-Metallacycles and Exploration of Their Reactivities

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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