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. 2023 Jul 12;145(27):14945-14951.
doi: 10.1021/jacs.3c04837. Epub 2023 Jun 30.

Efforts toward Synthetic Photosynthesis: Visible Light-Driven CO2 Valorization

Timothy D Schoch  1 , Jimmie D Weaver  1
Affiliations

Efforts toward Synthetic Photosynthesis: Visible Light-Driven CO2 Valorization

Timothy D Schoch et al. J Am Chem Soc. .

Abstract

Current methods of urethane preparation from amines invariably involve high-energy and often toxic or cumbersome molecules to make the process exergonic. CO2 aminoalkylation using olefins and amines represents an attractive albeit endergonic alternative. We report a moisture-tolerant method that uses visible light energy to drive this endergonic process (+25 kcal/mol at STP) using sensitized arylcyclohexenes. They convert much of the photon's energy to strain upon olefin isomerization. This strain energy greatly enhances alkene basicity, allowing for sequential protonation by and interception of ammonium carbamates. Following optimization steps and amine scope evaluation, an example product arylcyclohexyl urethane underwent transcarbamoylation with some demonstrative alcohols to form more general urethanes with concomitant regeneration of the arylcyclohexene. This represents a closure of the energetic cycle, producing H2O as the stoichiometric byproduct.

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Figures

Figure 1.
Figure 1.. Urethanes in medicines and materials.
(A) Urethanes with medicinal properties. (B) Some polymeric urethanes.
Figure 2.
Figure 2.. Conversion of primary and secondary amines to urethanes.
(A) Urethanes using CO as the C1 synthon. (B) Urethanes using CO as the C1 synthon along with either isocyanation (dehydrative) conditions or reactive electrophiles. (C) Urethane using activated olefin as proto-electrophile. (D) Urethanes from photon-strained olefin
Figure 3.
Figure 3.. Reactions performed with optimized urethane synthesis procedures in hand.
(A) Investigation of amine scope. Values reported are isolated percent yields with the isolated mass in parentheses. (B) Urethane from exhalation. (C) Base-mediated transcarbamoylation as urethane generalization strategy.
Figure 4.
Figure 4.. Urethanation Hammett Study.
k/kH determined from relative 19F NMR yields after 30 minutes irradiation.
Figure 5.
Figure 5.. Urethane Preparation as a Cyclic Process using Arylcyclohexenes as ‘Energy Currency’
Scheme 1.
Scheme 1.. Proof of Concept Urethane Synthesis.
See this image and copyright information in PMC

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