Biomass has received significant attention in the 21st century regarding its ability to become an alternative source of carbon for the production of strategic chemicals and fuels. Although multiple approaches for the selective valorization of biorefinery carbohydrates are known, processes of similar selectivity for the valorization of lignin are scarce, which can be attributed to its heterogeneity arising from its biosynthesis, as well as methods used for its isolation within the biorefinery. This perspective highlights advances within the last six years toward lignin valorization in the areas of thermochemical transformations, oxidations, reductions, and the tailoring of the lignin biosynthetic pathway in an effort to produce high-value chemicals and fuels. Should these current hurdles be addressed, significant progress can be made toward the realization of biomass replacing petroleum in meeting the world’s energy and chemical needs.

We describe an efficient five-step, enantioselective synthesis of (R,R)- and (S,S)-lignin dimer models possessing a β-O-4 linkage, by using the Evans chiral aldol reaction as a key step. Mitsunobu inversion of the (R,R)- or (S,S)-isomers generates the corresponding (R,S)- and (S,R)-diastereomers. We further extend this approach to the enantioselective synthesis of a lignin trimer model. These lignin models are synthesized with excellent ee (>99 %) and high overall yields. The lignin dimer models can be scaled up to provide multigram quantities that are not attainable by using previous methodologies. These lignin models will be useful in degradation studies probing the selectivity of enzymatic, microbial, and chemical processes that deconstruct lignin.

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