Carbon-carbon bond formation via a tandem cationic 2-aza-Cope rearrangement-Lewis acid promoted Petasis reaction

Potassium alkynyltrifluoroborates and potassium (2-phenyl)vinyltrifluoroborates react with N-3-butenyl-(2,2-dichloro-1-propylidene)amine in the presence of BF₃·Et₂O as a Lewis acid to synthesize rearranged Mannich products. The reaction starts with a cationic 2-aza-Cope rearrangement of the imine, followed by the Lewis acid promoted borono-Mannich-type reaction on the rearranged imine to result in a new class of functionalized N-homoallylamines.     

1,3-Polyol arrays via the stereoselective rearrangement of vinyl acetals

A series of 1,3-dioxanyl vinyl acetals were readily synthesized from the corresponding dioxanone by a reduction and in situ acylation followed by Petasis olefination. Treatment of these vinyl acetals with BF₃·OEt₂ results in an O to C rearrangement to form anti-3,5-dihydroxyketones while a mixture of Me₃Al and BF₃·OEt₂ provides the corresponding syn relationship via a stereoretentive rearrangement.     

Reactions of vinylidenecyclopropanes with xanthydrol and xanthene

Vinylidenecyclopropanes undergo ring-opening reactions with xanthydrol in the presence of BF₃·OEt₂ or with xanthene in the presence of DDQ at 0 °C in 1,2-dichloroethane to give the corresponding conjugate triene derivatives in moderate to good yields. Plausible reaction mechanisms have been discussed on the basis of previous literature and the control experiments. The further transformation of these trienes has been disclosed in DCE in the presence of BF₃·OEt₂ along with a plausible reaction mechanism.     

Lewis acid promoted Mannich type reactions of α,α-dichloro aldimines with potassium organotrifluoroborates

Potassium phenylethynyltrifluoroborate and potassium styryltrifluoroborates react with α,α-dichlorinated aldimines in the presence of BF₃·OEt₂ as a Lewis acid to give a new stable class of functionalized propargylamines and allylamines. The use of hexafluoroisopropanol as a co-solvent in this modified Petasis reaction allows high yield isolation of the target compounds.     

Efficient microwave-assisted synthesis of oximes from acetohydroxamic acid and carbonyl compounds using BF3·OEt2 as the catalyst

An efficient synthesis of oximes by reaction of carbonyls with acetohydroxamic acid using BF₃·OEt₂ as a catalyst is described.     

PEG-400 as green reaction medium for Lewis acid-promoted cycloaddition reactions with isoeugenol and anethole

A simple and efficient one-pot method for the synthesis of new 2,4-diaryl-1,2,3,4-tetrahydroquinolines using a three-component imino Diels-Alder cycloaddition between trans-isoeugenol or trans-anethole, anilines, and benzaldehyde in the presence of BF₃·OEt₂ in PEG-400, a green and reusable solvent, has been developed. Also, BF₃·OEt₂-catalyzed formal [3+2] cycloaddition reaction of trans-isoeugenol or trans-anethole with 1,4-benzoquinone in PEG-400 to give dihydrobenzo[b]furan derivatives has been described.     

A new and efficient one-pot synthesis of aromatic alkynyl ketones from aromatic esters

The reaction of aromatic esters with alkynyllithiums in the presence of lithium morpholinide and BF₃·OEt₂ gave aromatic alkynyl ketones in good yield (78-87%).     

A novel aza-Prins-Friedel-Crafts reaction for the synthesis of 4-arylpiperidines

Aldehyde, homoallylic amine and arene undergo smooth cyclization in the presence of BF₃·OEt₂ to afford 4-arylpiperidines in good yields and with high trans-selectivity. This is the first report on the preparation of 4-arylpiperidines via aza-Prins-Friedel-Crafts reaction.     

Improved Ritter reaction with CF3-containing oxirane for an access to central units of protease inhibitors

The influence of fluorinated alcohols on the BF₃·Et₂O-promoted Ritter type reaction has been investigated. Trifluoroethanol/BF₃·Et₂O system allowed access to the central unit of protease inhibitors by the ring opening of fluorinated epoxide 2 with various nitriles.     

Microwave-assisted aza-Cope rearrangement of N-allylanilines

The aza-Cope rearrangement of N-allylanilines is described. The use of BF₃·OEt₂ and microwave irradiation allows to run the transformation under mild conditions and in reaction times of minutes.     

Direct oxidative cyclization of 3-arylpropionic acids using PIFA or Oxone: synthesis of 3,4-dihydrocoumarins

The direct oxidative cyclization of 3-arylpropionic acids using PIFA or Oxone is reported. In the presence of BF₃·OEt₂, the reaction of 3-arylpropionic acids with PIFA or Oxone proceeded smoothly at 30 °C to give 3,4-dihydrocoumarins in good to excellent yields.     

Nucleophilic alkynylation of N-bis(trimethylsilyl)methyl aldimines

N-Bis(trimethylsilyl)methyl aldimines undergo nucleophilic addition reaction with premixed lithium alkynides/BF₃·OEt₂ to give moderate to good yields of N-bis(trimethylsilyl)methyl propargyl amines.     

Microwave-assisted aza-Prins reaction. Part 1: facile preparation of natural-like 3-azabicyclo[3.3.1]non-6-enes

A facile and operationally simple route to diastereomerically pure, natural-like 3-azabicyclo[3.3.1]non-6-enes via microwave-assisted, BF₃·OEt₂-promoted aza-Prins reaction has been developed. Complexity-generating transformations based on these products involving reactive functionalities introduced during the aza-Prins step have been developed.     

Boron trifluoride–etherate in fluorinated alcohols: A powerful promoter system for intramolecular alkyne–aldehyde metathesis of o-(3-arylpropargyloxy)benzaldehydes

Boron trifluoride–etherate (BF₃·OEt₂) in 2,2,2‐trifluoroethanol (TFE) was found to be a highly efficient promoter system for the intramolecular alkyne–aldehyde metathesis of o-(3-arylpropargyloxy)benzaldehydes. The reaction produces the corresponding 3-aroyl-2H-chromenes in excellent yields under metal-free conditions.     

BF3-promoted cyclization reaction of imines and salicylaldehyde with silyl enol ethers: unexpected formation of dioxaspiro compounds

Unexpected spiro cyclic products were formed from the reaction of imines and salicylaldehyde with silyl enol ethers in the presence of BF₃·OEt₂. Different kinds of dioxaspiro products were afforded depending on the nature of starting materials. Furthermore, salicylaldehyde could also react directly with several silyl enol ethers, giving three products with different spiro cyclic structure under the same reaction conditions.     

Oxidation of aldimines to amides by m-CPBA and BF3·OEt2

Several amides were obtained in high yields by an efficient method from the corresponding imines which are readily prepared from aldehydes. This procedure involves the oxidation of aldimines with m-CPBA and BF₃·OEt₂. In this reaction, the product is strongly influenced by the electron releasing capacity of the aromatic substituent.     

Synthesis of N,N-difluoroboryl complexes of 3,3′-diarylazadiisoindolylmethenes

N,N-Difluoroboryl complexes of 3,3′-diarylazadiisoindolylmethenes were synthesized by the reaction of BF₃·OEt₂ and 3,3′-diarylazadiisoindolylmethenes, which were easily prepared from a reaction between phthalonitrile and aryl Grignard reagents. These novel dyes exhibit strong absorption in the visible region and intense fluorescence in the vis/NIR region. Their synthesis, characterization, and optical properties are reported in this Letter.     

Microwave-promoted synthesis of polyhydroxydeoxybenzoins in ionic liquids

A microwave-promoted synthesis of polyhydroxydeoxybenzoins and -phenylpropanones has been developed, using bis{(trifluoromethyl)sulfonyl}amine (HNTf₂) or BF₃·OEt₂ in an ionic liquid solvent.     

BF3·OEt2-catalyzed intermolecular reactions of arylmethylenecyclopropanes with (E)-1,1,3-triarylprop-2-en-1-ols

BF₃·OEt₂-catalyzed intermolecular reactions of arylmethylenecyclopropanes with (E)-1,1,3-triarylprop-2-en-1-ols produced the corresponding triene compounds, alcoholic derivatives or cyclobutane derivatives in moderate to excellent yields under mild conditions.     

BF3·OEt2 mediated regioselective deacetylation of polyacetoxyacetophenones and its application in the synthesis of natural products

We have developed an efficient method to regioselectively deacetylate polyacetoxyacetophenones using BF₃·OEt₂ in excellent yields and demonstrated the application of the procedure in the synthesis of natural products.