This work explores the reactivity of a reversible superbase–CO ₂ zwitterion, which can be used as a stoichiometric source of CO ₂ .

We report the use of dual nickel photocatalysis in the synthesis of O-aryl carbamates from aryl iodides or bromides, amines, and carbon dioxide. The reaction proceeded in visible light, at ambient carbon dioxide pressure, and without stoichiometric activating reagents. Mechanistic analysis is consistent with a Ni(I-III) cycle, where the active species is generated by the photocatalyst. The rate-limiting steps were the photocatalyst-mediated reduction of Ni(II) to Ni(I) and subsequent oxidative addition of the aryl halide. The physical properties of the photocatalyst were critical for promoting formation of O-aryl carbamates over various byproducts. Nine new phthalonitrile photocatalysts were synthesized, which exhibited properties that were vital to achieve high selectivity and activity.

Titanium-mediated 1,2-activation of Grignard reagents enables α and β insertion of carbon dioxide and arylaldehyde to prepare cis-3,4 butyrolactones.

Conventional CO₂-based carboxylation of amino alcohols to cyclic carbamates is often hindered by poor chemo- and stereoselectivity, the need for high pressure or subzero temperatures, reliance on expensive or toxic reagents and catalysts, and the formation of hazardous waste. To address these limitations, we evaluated mild dehydrating reagents for their ability to promote the cyclization. Among the reagents tested, n-butyl chloride emerged as the optimal choice, offering a desirable combination of low cost, low toxicity, and high selectivity. In contrast to conventional highly reactive dehydrating reagents, n-BuCl provides high selectivity toward carbamate anion alkylation. Upon heating, the resulting linear carbamate intermediate cyclizes, liberating benign butanol and yielding almost exclusively stereoretentive five- and six-membered cyclic carbamates in 17–98% yields.