Revisiting the Mg/TMSCl/Dipolar Solvent System for Dearomatic Silylation of Aryl Carbonyl Compounds: Substrate Scope, Transformations, and Mechanistic Studies

Dearomatic silylation of arene derivatives is an intriguing synthetic target, which represents an elegant extension of Birch reduction and produces silylated cyclohexene derivatives with great potential of further transformation. Herein, we report a systematic study on dearomatic silylation of aryl carbonyl compounds with Mg and the TMSCl/NMP adduct. The protocol displays a wide range of substrate scope, including alkyl aryl ketones, aromatic amides, benzonitriles, tert-butyl benzoates, and even 2,2'-bipyridines. Synthetic utility is demonstrated using the products as versatile substrate in various transformations. The detailed mechanism is presented with both control experimental analyses and theoretical calculations. An unusual five-coordinated silicon dianion intermediate is first proposed and described here. The selectivity is influenced by the relative rates of single electron reductions (the TMSCl/NMP adduct versus the substrate) and the steric effects.

Photocatalytic Carbinol Cation/Anion Umpolung: Direct Addition of Aromatic Aldehydes and Ketones to Carbon Dioxide

We have developed a new photocatalytic umpolung reaction of carbonyl compounds to generate anionic carbinol synthons. Aromatic aldehydes or ketones reacted with carbon dioxide in the presence of an iridium photocatalyst and 1,3-dimethyl-2-phenyl-2,3-dihydro-1H-benzimidazole (DMBI) as a reductant under visible-light irradiation to furnish the corresponding α-hydroxycarboxylic acids through nucleophilic addition of the resulting carbinol anions to electrophilic carbon dioxide.

Light-Mediated Carboxylation Using Carbon Dioxide

Carbon dioxide is a green and sustainable one-carbon source, which could be utilized in the production of various fine chemicals. In recent studies, the light-mediated carboxylation employing CO₂ has received considerable attention. The photocarboxylation of substrates with CO₂ to build novel C-C bonds is introduced in this Minireview. The article is arranged based on the light-driven reactive intermediates, including CO₂ radical anion, substrate radical anions, carbanions, and M-C species. Most of the cases are under the topic of photoredox catalysis, with single electron transfer as the main driving force. Some non-catalytic examples are also discussed to provide more mechanistic insights.