Regio- and stereoselective coupling of dienes and alpha-olefins catalyzed by titanium aryloxide compounds
Abstract
The bis(aryloxide) substrates ((ArO)$\sb2$TiCl$\sb2$), (ArO = 2,6-diphenylphenoxide, 2,3,5,6-tetraphenylphenoxide, 2,6-diisopropylphenoxide, and 2,6-dimethylphenoxide) have been synthesized by the room temperature reaction of the corresponding phenol with titanium tetrachloride or via other methods. The addition of nBuLi, (the Negishi method typically applied to the Group 4 metallocene dichlorides), to these substrates produces an $\eta\sp2$ bound species upon $\beta$-hydride abstraction and reductive elimination. In the presence of unsaturated hydrocarbons, the in situ generated bis(aryloxide) titanium $\eta\sp2$ butene species catalyzes regio- and stereoselective coupling and cross-coupling reactions. This method is capable of an extremely rapid non-Diels Alder dimerization of 1,3-cyclohexadiene to produce a single product (17) which has not been made by thermal or photochemical methods. The cross-coupling of 1,3-cyclohexadiene with vinyltrimethylsilane has also been carried out by this method to produce substituted 1,3-cyclohexadiene products (23), (24). These observations strongly indicate that elimination from titanacyclopentane rings is accelerated by the presence of $\alpha$-vinyl groups. The cis-1,4-hydrovinylation of cycloocta-1,3-diene with $\alpha$-olefins has also been carried out by this method to produce substituted cyclooct-3-ene products (27-30). The lack of formation of conjugated cycloocta-1,3-diene products may be a result of the greater conformational flexibility of the eight membered ring making abstraction of the ring hydrogen more difficult.
Degree
Ph.D.
Advisors
Rothwell, Purdue University.
Subject Area
Chemistry|Organic chemistry
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