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

Abstract

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

An effective Pd nanocatalyst in aqueous media: stilbene synthesis by Mizoroki–Heck coupling reaction under microwave irradiation

“…The products were characterized by 1 H NMR, 13 C NMR, and GC–MS. All the spectroscopic data were in agreement with those previously reported for the following compounds: ( E )-1,1'-(ethene-1,2-diylbis(4,1-phenylene))diethanone ( 17 ) [ 68 ] and ( E )-1,2-bis(3,5-dimethoxyphenyl)ethane ( 18 ) [ 69 ].…”

The Nugent Reagent: A Formidable Tool in Contemporary Radical and Organometallic Chemistry

“…Barrero et al49 reported that the Nugent reagent was able to induce reductive carbonyl coupling with short reaction times and total reproducibility. The reported mechanistic evidence established the involvement of Ti III pinacolates in the deoxygenation step of this McMurry olefination for the first time (Scheme ).…”

Palladium nanoparticles supported on reduced graphene oxide as an efficient catalyst for the reduction of benzyl alcohol compounds

“…of Ti(III) and 1.5 equiv. of reducing agent such as Mn dust in tetrahydrofuran as solvent [7]. Recently, direct electrolysis of primary alcohols in excess of methyl toluate was reported for the synthesis of the corresponding deoxygenated products in high yield [8].…”