A density functional theory investigation on bis(diethylamino)cyclopropenylidene catalyzed synthesis of 1,4‐bifunctional compounds

Abstract

Bis(amino)cyclopropenylidenes (BACs) are the newly discovered umpolung catalysts with potential applications in the synthesis of numerous important organic moieties. A plausible mechanism for bis(diethylamino)cyclopropenylidene (Et‐BAC) catalysed synthesis of 1,4‐diketones has been investigated using density functional theory (DFT). The proposed catalytic cycle initiates with the nucleophilic interaction of in situ generated Et‐BAC with p‐methoxybenzaldehyde to form a zwitterionic intermediate, which on proton transfer reaction gives Breslow intermediate. Breslow intermediate then favours 1,4‐umpolung addition reaction with chalcone followed by another proton transfer to regenerate the Et‐BAC along with enolic form of the product. Enolic form ultimately transforms into the desired keto form, 1‐(4‐methoxyphenyl)‐2,4‐diphenylbutane‐1,4‐dione via protonated and free DBU aided proton shift mechanism. DFT‐derived reactivity parameters along with frontier molecular orbital (FMO) analysis have been successfully utilised to reveal the umpolung efficacy of Et‐BAC. This DFT exploration is in good accordance with experimental findings and also offers a deeper insight into the Et‐BAC catalysed organic transformations.