Alkene Synthesis by Photocatalytic Chemoenzymatically Compatible Dehydrodecarboxylation of Carboxylic Acids and Biomass

Abstract

Direct conversion of renewable biomass and bioderived chemicals to valuable synthetic intermediates for organic synthesis and materials science applications by means of mild and chemoselective catalytic methods has largely remained elusive. Development of artificial catalytic systems that are compatible with enzymatic reactions provides a synergistic solution to this enduring challenge by leveraging previously unachievable reactivity and selectivity modes. We report herein a dual catalytic dehydrodecarboxylation reaction that is enabled by a crossover of the photoinduced acridinecatalyzed O−H hydrogen atom transfer (HAT) and cobaloxime-catalyzed C−H-HAT processes. The reaction produces a variety of alkenes from readily available carboxylic acids. The reaction can be embedded in a scalable triple-catalytic cooperative chemoenzymatic lipase−acridine−cobaloxime process that allows for direct conversion of plant oils and biomass to long-chain terminal alkenes, precursors to bioderived polymers.

Visible‐Light‐Enabled Direct Decarboxylative N‐Alkylation

“…Other solvents (toluene and trifluorotoluene) were also potentially suitable, and LED light with λ max =420 nm could also be used. Additionally, the reaction was not sensitive to air, underscoring the practicality of the acridine‐photocatalyzed decarboxylation, and in agreement with prior mechanistic conclusions that acridines effect the photocatalytic decarboxylation via the singlet excited state …”

Photoredox/Cobalt Dual‐Catalyzed Decarboxylative Elimination of Carboxylic Acids: Development and Mechanistic Insight

“…These results seem to suggest that the unsubstituted and quaternary acids interrupt the catalytic cycle . This stands in stark contrast to the reports by Ritter, Larionov, and Liu/Wu; much of their substrate scope and highest yields were derived from unsubstituted carboxylic acids.…”

“…However, the Heck‐type methodology of Liu/Wu (Scheme E) does benefit from the use of a catalytic amount of base. Presumably, the base is generating the carboxylate reductant and could also help establish an equilibrium between Co III hydride and Co I …”

“…Another approach, simultaneously developed by the Ritter group and our lab, involves the direct decarboxylation of the carboxylic acids followed by subsequent elimination through the combination of decarboxylation and hydrogen evolution (Scheme B,C) . Shortly thereafter, Larionov reported a decarboxylative elimination of biomass‐derived feedstocks utilizing various acridine/cobaloxime dual‐catalytic systems (Scheme D) . In addition, Liu/Wu report a similar decarboxylative elimination process in a Heck‐type coupling (Scheme E) .…”

Cross-Coupling Hydrogen Evolution Reactions

“…在可见光照射下, 烷基羧酸与乙烯基芳烃、杂芳烃、硅 烷、硼酸酯等均可顺利发生 Heck 类型的偶联; 烷基羧 酸、丙烯酸酯、乙烯基芳烃之间甚至可实现三组分偶联 反应 [18] . 此外, 烷基羧酸自身在可见光驱使放氢偶联体 系中也能消除二氧化碳和氢气, 生成重要的化工原料烯 烃 [19,20] . 上述转化若采用传统的氧化脱羧方法, 则需要 较高的反应温度和当量或过量的氧化剂, 以及考虑氧化 剂残渣的分离和无污染处理.…”