Development of Highly Efficient Methods for the Construction of Carbon Frameworks Utilizing Titanium-Carbene Complexes

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In this study, new methods for the construction of fundamental carbon frameworks utilizing titanium-carbene complexes, prepared by the desulfurizarion of thioacetals with titanocene(II) species, were explored.1. Intermolecular reactions of titanium-carbene complexesThe reaction of carbene complexes with nitriles proceeded via the formation of azatitariacyclobutene to produce acylation products in good yields. The treatmant of vinylcarbene complexes with tert-halides gave the vinyltitanium species, which reacted with terminal alkynes and aldehydes to produce the corresponding adducts. Various allylsilanes were prepared by the reaction of the carbene complexes generated from 1,3-bis(phenylthio)propenes possessing a trialkylsilylmethyl group.2. Intramolecular reactions of titanium-carbene complexesThioacetals bearing a carbon-carbon double bond afforded the unsaturated cyclic compounds via the ring-closing metathesis process when being treated with titanocene(II) species. This reaction wa … More s successfully applied to the synthesis of various heterocycles such as cyclic amines, ethers, and sulfides. The ring-closing metathesis and subsequent oxidative cleavage of unsaturated thioacetals possessing a silyl ether moiety gave the Z-1 ,5-olefmic diols with high stereoselectivity. It was found that the esters and thiolesters bearing a thioacetal moiety were good substrates for the intramolecular carbonyl olefination giving a variety of unsaturated cyclic compounds. Using this method, regioselective preparation of enol ethers of cyclic ketones, synthesis of dihydrothiophenes, and transformation of carboxylic acids into o-hydroxy ketones have been achieved.3. Reaction of organotitanium species generated from organic halides and titanocene(II)The treatment of gem-dihalides having a terminal carbon-carbon double bond with the titanocene(II) species produced the bicyclic cyclopropanes. The 1,2-disubstituted cyclopropanes were also produced with high trans-selectivity by the reaction of 1,3-dihalides with the titanocene(II) reagent. Less