Photo-catalyst-free photomediated pinacol coupling of ketones/aldehydes by formate at room temperature

Abstract

In this work, a highly effective metal-free and photo-catalyst-free method for the reductive coupling of carbonyl compounds to produce pinacols using formate under photoirradiation has been reported. This method exploits the highly reactive carbon dioxide radical anion (CO₂˙⁻) as an electron reductant, which is accessed through the homolytic cleavage of the C–H bond of HCOO⁻ by 365 nm light at room temperature. Mechanistic investigation revealed that the cleavage of the C–H bond of formate takes place under 365 nm light, resulting in the formation of CO₂˙⁻ and H˙. Notably, in batch reactions a 20 g-scale of substrates can be converted to the corresponding pinanols with quantitative yields. The advantages of this approach include a wide range of substrate compatibility, high efficiency, ease of operation, and environmentally friendly attributes, making it a promising strategy for industrial applications.