Bioinspired Photocatalyzed Organic Synthetic Transformations. The Use of Natural Pigments and Vitamins in Photocatalysis

Abstract

Due to the necessity for more environmentally benign processes in synthetic organic chemistry, and in particular in photocatalysis, a recourse to photocatalysts that are also found in nature and mimic natural processes to accomplish organic transformations is very appealing. Synthetic useful reactions such as oxidations, reductions, carbon-oxygen, carbon-carbon and carbon-sulfur bond formation reactions, and E-to-Z geo-metrical isomerization reactions photocatalyzed by biological natural pigments, vitamins, cofactors, and compounds with antiviral activity will be discussed in this account. Interestingly, due to the remarkable redox properties and triplet energies of some of these catalysts that are found in nature, both electron transfer (ET)-and energy transfer (EnT)-driven photocatalytic processes can be accomplished.

Vitamin B12 in Photocatalysis – An Underexplored Frontier in Cooperative Catalysis

“…It has also been observed in the circulatory and nervous systems [10b] . One functionality of interest was observed in the bacterial cells of M. Xanthus and T. Thermophilus , wherein VB 12 acts in conjunction with the CarH photoreceptor in light‐dependent gene regulation to activate carotenoid formation [10a,11] . The formation of these carotenoids is significant due to their ability to quench any oxygen species formed from light exposure, thereby protecting the bacteria cell from photo‐oxidative damage [11b] …”

“…A second, and commonly used application of VB 12 reactivity in synthesis, is a homolytic, single‐electron process for cleavage or formation of a Co−C bond. Further showcasing its reactive flexibility, VB 12 can act as a reversible radical carrier or nucleophile, depending on its oxidation state [10a,12] . A common mechanism of VB 12 in synthesis generally uses the following scheme: VB 12 ’s Co(III) center is reduced to Co(I), forming a supernucleophile.…”

Vitamin B12 and hydrogen atom transfer cooperative catalysis as a hydride nucleophile mimic in epoxide ring opening

“… 16 We were drawn to VB 12 as a photocatalyst as it is a naturally occurring, widely available cobalt complex with a wide range of ionic and radical reactivity ( Figure 2A ) that has been used by nature and synthetic chemists alike to achieve many powerful transformations. 17 – 20 …”

Photocatalytic Transformation of Biomass and Biomass Derived Compounds—Application to Organic Synthesis

“…In particular, photocatalysis with visible light is now investigated [42,43]. The systematic study of these reactions opens perspectives for organic synthesis [44,45]. The generally mild photochemical reaction conditions facilitate a large number of C-H activation processes.…”