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Application of DBU in organic synthesis

October 24, 2022by admin0
DBU is a large-site resistive amidine organic base, whose two adjacent nitrogen atoms can serve to stabilize the protonation site. As a non-nucleophilic organic base, its involvement in reactions can effectively avoid side reactions due to the nucleophilic nature of the base, but there are a few literature reports of DBU being used as a nucleophilic base. Because of its cheap and easy availability, good solubility in organic solvents and easy recovery, DBU is often used as catalysts, complexing ligands and nucleophilic or non-nucleophilic bases in a wide range of organic reactions.
The following is a brief review of the organic reactions in which DBU is involved.
Elimination reaction
DBU is capable of removing hydrogen halides and sulfonic acids. It can achieve the conversion of sulfonic acid esters to olefins via the one-pot method of iodinated hydrocarbons.
Isomerization reaction
DBU can convert β,γ-unsaturated carbonyl compounds into more stable ɑ,β-unsaturated carbonyl compounds.
Halogenation Reactions
DBU as a base, dichloromethane as a solvent, and NCS or (PhSO2)2NF / Selectfluor can be used to achieve the dihalogenation of vinyl or phenyl nitromethane methylene.
DBU-HBr3 is often used as a mild, stable and recyclable bromine reagent for the bromination of many aromatic hydrocarbons.
Esterification reaction
DBU and dimethyl carbonate (DMC) produce carbamate intermediates, which can react with carboxylic acids to produce the corresponding methyl esters.
Amidation reaction
DBU-NHC (N-heterocycliccarbene) can be reacted with ɑ-substituted aldehydes to form the corresponding amides.
Carbonylation reaction
DBU as a catalyst can achieve the methoxycarbonylation of alcohol hydroxyl groups even in the presence of phenolic hydroxyl groups.
Condensation reactions
DBU-H2O is a very effective catalytic system for Aldol condensation reactions, however, DBU alone cannot catalyze such reactions.
Horner-Wadsworth-Emmons reaction
The Horner-Wadsworth-Emmons reaction is a variant of the Wittig reaction and is commonly used for the synthesis of ɑ,β-unsaturated esters. DBU is often used as the base for this reaction, and the E-form product can be obtained in high yield under solvent-free conditions.
Nef reaction
Using DBU as a base, it can selectively react many seco-carbon nitroalkanes.

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