Titanium-Catalyzed Deoxygenation of Alcohols and Valorization of Biomass

Abstract

The deoxygenation reaction represents a useful transformation for both synthetic applications and industrial scale processes, like the valorization of biomass or the synthesis of bioactive compounds. Therefore, the pursuit of more robust and cost effective homogenous deoxygenation procedures attracts great interest. In the first part of this presentation, the optimization attempts of a previously reported Pd-based deoxygenation methodology will be discussed. During this process, the influence of multiple reaction parameters was studied in order to increase the applicability of the system and to gain more insight into the reaction pathway. In the second part of this report, the development of new non-precious-metal based deoxygenation procedures was endeavoured, namely Ti- and Co-based catalytic systems. The most efficient for the desired transformation proved to be the Ti-based system in which alkoxyhydrosilanes, triethoxysilane and methyldiethoxysilane, were utilised as H-donors. The H-donor capabilities of Hantzsch esters were also tested in the Ti-catalysed methodology and, although they proved to be efficient for the generation of the desired products, the yields were lower compared to the Ti-hydrosilane system. Primary and secondary benzylic alcohols, bearing various non-participating functional groups, were efficiently reduced through this methodology. Besides, this catalytic system proved to be effective in the reduction of olefins, diols, carbonyls, esters and thioesters. Additionally, it is shown that this system can be applied for the reduction of lignin building blocks and lignin model substrates. The deuteration, radical clock, and radical scavengers experiments revealed that the reaction follows a radical pathway.