Introduction of a common acid-base reagent --- Boron Trifluoride Etherate Complex

BF3-OEt2 is a common and easy to handle alternative to BF3. As Lewis acid, it can catalyze ring opening and rearrangement of epoxides, esterification of carboxylic acids, and breakage of Trityl ethers, etc.

 

【English name】Fuel Additive

【Molecular Formula】C4H10BF3O

【Molecular Weight】141.94

【CA Registry Number】109-63-7

【Abbreviation and Alias】Boron Trifluoride Diethyl Etherate, Boron Trifluoride Ethyl Etherate, Boron Trifluoride Ether Complex

【Physical properties】Bright yellow liquid, bp 126 °C, 1.15g/cm3. soluble in most organic solvents, such as benzene, toluene, various chloromethanes, ether, methanol, 1,4-dioxane and tetrahydrofuran. Usually used in dichloromethane.

【Preparation and commodity】It is sold by domestic and foreign reagent companies, and generally not prepared in the laboratory.

【Precautions】It can be slowly oxidized in air and turn black. It is better to be purified by distillation before use. It is sensitive to moisture and will react violently with water to release toxic fluorinated gas. Must be used in anhydrous system and operated in a fume hood.

 

BF3-OEt2 is a common and easy to handle alternative to BF3. As Lewis acid, it can catalyze ring opening and rearrangement of epoxides, esterification of carboxylic acids, and breakage of Trityl ethers, etc.

As Lewis acid, BF3-OEt2 is commonly used in a variety of nucleophilic addition reactions to enhance the reactivity of nucleophilic reagents. In the presence of BF3-OEt2, the reactivity of TMSCN, allylsilyl reagents, alkylcopper lithium reagents and allyl silyl ethers is significantly enhanced. For example, under mild conditions, allylsilyl reagents can undergo SN2 substitution reactions on Morial-Baylis-Hillman addition products with high yields and high cis-trans selectivity to produce 1,5-diene derivatives (Eq. 1).

 

 

BF3-OEt2 is also commonly used to catalyze the Diels-Alder addition reaction between furan and methyl acrylate, yielding products with good endo-selectivity. It can also catalyze heteroatomic cycloaddition reactions between aldehydes and enol silyl ethers to yield pyrone derivatives (pyrones). The stereoselectivity of this reaction can also be effectively controlled by the choice of a suitable solvent (Eq. 2).

 

 

BF3-OEt2 is also commonly used in many reactions for the generation and removal of protecting groups. In nonprotonic solvents, BF3-MeOH gently removes Trityl ether bond protection with good functional group compatibility, and BF3-OEt2, when used with iodide ions, gently breaks alkyl ether bonds and removes acetal protection. Unlike other acidic boron reagents, aromatic ethers do not break under these conditions. In chloroform or dichloromethane, BF3OEt2 can catalyze the removal of TBDMS protection.

Its ethanol solution is widely used for the esterification of various alkyl or aryl carboxylic acids, and some less stable substrates can be esterified under this mild condition. In addition, it is also used for the condensation of carboxylic acids with amines to form amides, which can be accelerated by the addition of bases or azeotropic partitions of water.

At room temperature, BF3-OEt2 catalyzes the Beckmann rearrangement of various ketoxime carbonates to give amides in good yields (Eq. 3).

 

 

BF3-OEt2 can also catalyze the Beckmann rearrangement of silyl-protected ketoximes under the co-collaboration of borane. Due to the reduction of borane, the reaction directly produces various aniline derivatives (Eq. 4).

 

 

BF3-OEt2 can also catalyze Pinacol coupling reactions. Crossed Pinacol coupling reactions of imines and aldehydes can be catalyzed by the reduction of Zn-Cu alloys under the co-catalysis of trichloromethylsilane and BF3-OEt2 to give o-aminol compounds, but the stereoselectivity is not so good (Eq. 5). This system can also catalyze cross-coupling reactions between two imines with a greater improvement in stereoselectivity (Eq. 6).

 

 

BF3-OEt2 is also commonly used to catalyze a variety of reduction reactions. Unlike metal halides, BF3-OEt2 can catalyze the in silico hydrogenation of aldehydes and ketones at room temperature, with alkyl aldehydes and ketones yielding mainly ethers and boronic esters. In contrast, aryl ketones such as acetophenone or benzophenone are converted to ethylbenzene and diphenylmethane. BF3-Et2O is used together with NaBH4 for the reduction of a variety of carboxylic acid derivatives such as chlorides, esters, amides, cyano and carboxylic acids. Any imine can be reduced by tributyltin hydrogen under the catalysis of BF3-Et20.