Reductive CO 2 Homocoupling: Synthesis of a Borylated C 3 Carbohydrate

To use carbon dioxide as a source of carbon, recent progress has been made toward the synthesis of higher value chemicals and in particular toward Cn compounds. In this context, we report here the synthesis of a borylated C 3 ‐carbohydrate from CO 2 as the only source of carbon. This result corresponds to the unprecedented formation of a polyol chain and of asymmetric carbon atoms from CO 2 . The adopted strategy involves the Fe‐catalysed selective 4e − reduction of CO 2 into bis(boryl)acetal followed in one‐pot by a carbene‐mediated C−C coupling reaction. Boron is shown to play a key role in the coupling step enabling to observe the first diastereoselective formose‐type reaction. This result is in addition obtained under mild reaction conditions (T<80 °C, 1 atm of CO 2 ) and short reaction time (t<2 h).