Weakening C−O Bonds: Ti(III), a New Reagent for Alcohol Deoxygenation and Carbonyl Coupling Olefination

摘要

Investigations detailed herein, including density functional theory (DFT) calculations, demonstratenthat the formation of either alkoxy- or hydroxy-Ti(III) complexes considerably decreases the energy ofnactivation for C-O bond homolysis. As a consequence of this observation, we described two new syntheticnapplications of Nugent’s reagent in organic chemistry. The first of these applications is an one-stepnmethodology for deoxygenation-reduction of alcohols, including benzylic and allylic alcohols and 1,2-ndihydroxy compounds. Additionally, we have also proved that Ti(III) is capable of mediating carbonylncoupling-olefination. In this sense, and despite the fact that for over 35 years it has been widely acceptednthat either Ti(II) or Ti(0) was the active species in the reductive process of the McMurry reaction, thenmechanistic evidence presented proves the involvement of Ti(III) pinacolates in the deoxygenation step ofnthe herein described Nugent’s reagent-mediated McMurry olefination. This observation sheds some lightnon probably one of the mechanistically more complex transformations in organic chemistry. Finally, wenhave also proved that both of these processes can be performed catalytically in Cp2TiCl2 by usingntrimethylsilyl chloride (TMSCl) as the final oxygen trap.