Reductive CO₂ Homocoupling: Synthesis of a Borylated C₃ Carbohydrate

Abstract

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 C3‐carbohydrate from CO2 as the only source of carbon. This result corresponds to the unprecedented formation of a polyol chain and of asymmetric carbon atoms from CO2. The adopted strategy involves the Fe‐catalysed selective 4e− reduction of CO2 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 CO2) and short reaction time (t<2 h).

A Masked Form of an O‐Borylated Breslow Intermediate for the Diastereoselective FLP‐Type Activation of Aldehydes

“…The magnitude of these coupling constants is indicative of a 1,2-trans relative configuration (Scheme 2). Interestingly, when compound 2 a, isolated from the reaction of 1 and 2, [10] was reacted with benzaldehyde, the same diastereoselectivity was observed with the formation of 4 (Scheme 3).…”

Formaldehyde as a Promising C1 Source: The Instrumental Role of Biocatalysis for Stereocontrolled Reactions

“…Although those features have attracted interest in the fields of synthetic as well as prebiotic chemistry, understanding and control of this reaction remains largely unsolved challenges. 109 Biocatalyzed transformations are powerful answers to these specific issues, because enzymes afford high selectivity, stereospecificity and stereochemical complementarity. 9,36 The examples described in this publication show that aldol and umpolung reactions leads to complex valueadded products with perfect stereocontrol and without the need for protective groups.…”

Enantioselective Reductive Oligomerization of Carbon Dioxide into l-Erythrulose via a Chemoenzymatic Catalysis

“…The intrinsic difficulty in conducting each step (i.e., 4e – reduction of CO 2 and HCHO oligomerization) and associating two different catalytic processes certainly explain why such a formaldehyde strategy (Scheme a) has not been further explored for the synthesis of carbohydrates, until our findings using an N-heterocyclic carbene (NHC, Scheme b). We indeed recently reported the catalytic generation of glycolaldehyde (GA) and the stoichiometric generation of a borylated C 3 carbohydrate from CO 2 as the sole carbon source.…”