Direct Deoxydehydration of Cyclic trans‐Diol Substrates: An Experimental and Computational Study of the Reaction Mechanism of Vanadium(V)‐based Catalysis**

Abstract

The deoxydehydration of carbohydrates represents a key target to leverage renewable biomass resources chemically. Using a vanadium(V)‐based catalyst, it was possible to directly deoxydehydrate cyclic trans‐diol substrates. Accompanying mechanistic characterisation of this process by density functional calculations pointed to an energetically tractable route for deoxydehydration of cyclic trans‐diol substrates involving stepwise cleavage of the diol C−O bonds via the triplet state; experimentally, this was supported by light dependence of the reaction. Calculations also indicated that cyclic cis‐diols and a linear diol substrate could additionally proceed by a concerted singlet DODH mechanism. This work potentially opens a new and cost‐effective way to efficiently convert carbohydrates of trans‐diol stereochemistry into alkenes.

Reactivity of metal dioxo complexes

“…While exploring the inhibition of reactivity by ring strain, Bryce and coworkers found that alkene yields were substantially lower in the absence of ambient light. 15 Intersystem crossing events and stepwise olefin extrusion have been previously explored and are supported by DFT 16 but explicit enhancement of yield by light are shown here. The yields of cyclic cis and trans diols were still low (<20%), but enhancements of up to 5× were observed for reactions performed in light versus dark conditions.…”

Selective Biocatalytic Defunctionalization of Raw Materials

“…Reactions for upgrading biobased polyhydroxylated compounds by the selective removal of hydroxy groups are of great interest, for example, in deoxydehydration, [133][134][135][136][137] hydrodeoxygenation, [138,139] didehydroxylation, [140] or dehydrative epoxidation [141] of vicinal diols. While impressive advances have been achieved with various chemocatalysts, both transition metalbased and metal-free, further research and development is clearly needed for improving the selectivity, outcome, and sustainability of these reactions, such as high-performing, stable, and sustainable catalysts, additives, and solvents, in order to design industrially viable biobased processes.…”

Transition metal-catalyzed deoxydehydration: missing pieces of the puzzle

“…The proposed cycle involved several spin crossovers and consisted of diolate formation, reduction by triphenylphosphane, formation of a metallacycle and cleavage. Aksanoglu et al 160 revisited [VO 2 (dipic)] − -catalyzed DODH. At the M06-L/SDD/6-311+G**/SMD level, they found the barrier for reaction initiation by diolate formation to be 96 kJ mol −1 lower than that for initiation by reduction.…”

“…Recently, Aksanoglu et al 160 compared yields obtained in the dark and in the presence of visible light under exclusion of UV light by the use of borosilicate glass. They found a [ n -Bu 4 N]V(dipic)O 2 catalyst to give consistently higher olefin yields in the presence of light.…”