Selective,one-pot synthesis of 2,3,6-trisubstituted pyridine and 2-cyclohexen-1-one derivatives from bicyclic ketals

Boron difluoromethanesulfonate, prepared from 5 equivalents of trimethylsilyl methanesulfonate and 1 equivalent of boron trifluoride etherate, has proved to be an active Lewis acid catalyst for the one-pot transformation reaction of bicyclic ketals in the 6,8-dioxabicyclo[3.2.1]octane series to 2,3,6-trisubstituted pyridine or 2-cyclohexen-1-one selectively, depending on conditions. A 1,5-diketone was the reaction intermediate for both products. Pyridine was formed selectively by using a nitrile as a solvent or a reagent, but cyclohexenone was prepared in methylene chloride instead of a nitrile.     

Addition von organomagnesium-verbindungen an nicht aktivierte CC-doppelbindungen : IV. Benzylmagnesiumchlorid und olefine

Benzylmagnesium chloride (I) adds to ethylene and 1-alkenes, to the strained CC double bonds in bicyclo[2.2.1]hept-2-ene and bicyclo[2.2.1]heptadiene and to 1,3-alkadienes if the reaction of the etherate of (I) with olefin is carried out in an apolar reaction medium between 60 and 130°. Reaction products of the mono-olefins are the 1,1-adducts; derivatives of divinylcyclohexane are formed with butadiene as 1,3-adducts. With bicyclo[2.2.1]heptadiene the addition of the magnesium compound is followed by an intramolecular MgC-addition to the second double bond forming 2-benzyltricyclo[2.2.1.0¹]hept-3-ylmagnesium chloride.     

Development of efficient Lewis acid catalysts for intramolecular cycloaddition reactions of ester-tethered substrates

We have developed novel bidentate Lewis acids that efficiently promote the intramolecular cycloaddition reactions of ester-tethered substrates. Bis-aluminated triflic amide derivatives [TfN(AlR(1)R(2))2], which are generated by simply mixing triflic amide and 2 equiv of methyl aluminum or aluminum hydride, catalyzed intramolecular Diels-Alder (DA) reactions of ester-tethered 1,7,9-trienes and intermolecular DA reactions of alpha,beta-unsaturated lactones. We also found that bimetallic Lewis acid derived from 1,1'-biphenyl-2,2'-di(triflyl)amide and dimethylaluminum chloride promoted the intramolecular [3 + 2] cycloaddition reaction of acrylate derivatives having an allylsilane part.     

1,3-Diastereocontrol in acyclic radical allylations

The radical allylation of an acyclic α-hydroxyketone with allyltributyltin under chelation-controlled conditions is reported. Several reaction conditions were explored, including radical initiators, solvents, and temperatures to improve the yield and the diastereomeric ratio. Some Lewis acids, like magnesium bromide etherate and zinc chloride, gave superior diastereomeric ratios (up to 100:1) and good yields.     

New method for the synthesis of macrocyclic compounds

The intramolecular acylation of acid chlorides of ω-thienylalkanoic acids of various structures in the presence and absence of silica gel was investigated. The reaction of aluminum chloride etherate and the indicated acid chlorides with the surface groups of silica gel was studied by IR spectroscopy, and the role of the compounds formed on the surface in the reaction under consideration was discussed. A sequence of processes and a mechanism involving participation of the solid phase in the intramolecular acylation of acid chlorides of ω-thienylalkanoic acids are formulated.     

Reaction of acetyloxiranes with acetonitrile

2-Acetyloxiranes react with acetonitrile in the presence of equimolar amounts of Lewis acids. It was established that the use of boron trifluoride etherate or sulfuric acid as the catalyst leads to 2,7- and 3,6-diepoxy-1,5-dioxocanes, the use of aluminum trichloride, as well as stannic chloride, leads to the corresponding chlorohydrins, while the use of gaseous boron trifluoride leads to 2-oxazolines in satisfactory yields. It is shown that the reaction is regio- and stereospecific and that the resulting substituted 2-methyl-5-acetyl-2-oxazolines have a cis configuration.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No, 8, pp. 1022–1024, August, 1982.     

Reagent-controlled stereoselective synthesis of lignan-related tetrahydrofurans

The reaction of ring-closing metathesis-derived cyclic allylsiloxanes 3 with aldehydes in the presence of a Lewis acid gives 2,3,4-trisubstituted tetrahydrofurans related to the furanolignan family of natural products. The reactions proceed with complete 3,4-trans stereoselectivity, whereas the C-2 stereochemistry depends on both the aldehyde and Lewis acid used. When boron trifluoride etherate is used with aliphatic or electronically neutral aryl aldehydes, the reactions favor the production of the 2,3-cis isomer 8, whereas electron-rich aryl aldehydes lead to the 2,3-trans isomer 9 by Lewis acid-mediated isomerization of the kinetically favored cis isomer. The isomerization can be avoided by use of TMSOTf as a promoter, and hence, the stereochemistry can be tuned by appropriate choice of reagent. Cleavage of the pendant 3-ethenyl group installs the 3-hydroxymethyl group common to the furanolignans.     

Intramolecular ionic Diels-Alder reactions of alpha-acetylenic acetals

The intramolecular ionic Diels-Alder reaction of alpha-acetylenic acetals as a precursor of the propargyl cation has been investigated in the presence of Lewis acids and in protic acids. The reaction of diene-tethered alpha-acetylenic acetals (1-2) with formic acid yielded the regioselective intramolecular ionic Diels-Alder reaction products, bicyclodienal (9) and bicyclodienone (11) derivatives, in good yields.     

Synthesis and some transformations of thioesters of thienylacrylic acid

A number of thioesters of thienylacrylic acid were obtained by the condensation of 2-formylthiophene and 5-bromo-2-formylthiophene with acetylenic thioethers in the presence of boron trifluoride etherate. The reaction of the condensation products with hydrazine hydrate is accompanied by intramolecular cyclization to form the corresponding pyrazolines. The IR spectra of the synthesized compounds are discussed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1348–1349, October, 1971.     

Synthetic applications of azolium ylides to a traceless solid-phase synthesis of 2-substituted azoles

A new approach for the preparation of 2-substituted azole libraries using a polystyrene-carbamyl chloride resin in a traceless fashion is described. Azole substrates II are assembled in a one-pot condensation reaction of azoles and aldehydes with a resin-bound carbamyl chloride. Treatment of the azolyl-carbamate II with boron trifluoride etherate under thermal or microwave-assisted solvolysis conditions afforded 2-substituted azoles. [reaction: see text]     

Reaction of β-pinene and thiols in the presence of Lewis acids

The reaction of β-pinene with thiols using zinc chloride catalyst occurred regiospecifically to synthesize pinane-type sulfides and to form anti-Markovnikov addition products. However, the pinane structure isomerized into menthane in the presence of boron trifluoride etherate. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 146–148, March–April, 2006.     

Chiral Lewis acid-catalyzed enantioselective intramolecular carbonyl ene reactions of unsaturated alpha-keto esters

[reaction: see text] Chiral Lewis acid-promoted highly enantioselective intramolecular carbonyl ene reactions of unsaturated alpha-keto esters have been investigated. In the presence of chiral Lewis acids such as [Sc((R,R)-Ph-pybox)](OTf)(3) and [Cu((S,S)-Ph-box)](OTf)(2), several unsaturated alpha-keto esters underwent carbonyl ene reactions in CH(2)Cl(2) at room temperature to give monocyclic products in good yield and excellent enantioselectivity.     

Novel synthesis of 2-(trifluoromethyl)- and 2-(perfluoroalkyl)-2-hydroxy-2H-chromenes and their regiospecific reaction with silyl enol ethers

The synthesis of substituted 2-(trifluoromethyl)- and 2-(perfluoroalkyl)-2-hydroxy-2H-chromenes 2a-o was achieved in good yields by intramolecular cyclization of 3-(perfluoroalkyl)-3-phenoxypropenals 1 in the presence of aluminum chloride. Then a Lewis acid mediated nucleophilic reaction with silyl enol ethers 3 proceeded with complete regiospecificity to afford 4-functional 2-(trifluoromethyl)- and 2-(perfluoroalkyl)-4H-chromenes 4a-p with high yields.     

A synthesis of 3-phenyl-1,2,3,4-tetrahydroisoquinoline and 2-phenyl-1,2,4,5-tetrahydro-3H-3-benzazepine via Pummerer-type cyclization: enhancing effect of boron trifluoride diethyl etherate on the cyclization

A synthesis of 6,7-dimethoxy-3-phenyl-1,2,3,4-tetrahydroisoquinoline (14a) and 7,8-dimethoxy-2-phenyl-1,2,4,5-tetrahydro-3H-3-benzazepine (14b) was achieved via the cyclization of N-(3,4-dimethoxyphenyl)methyl-1-phenyl-2-(phenylsulfinyl)ethylformamide (6a) and N-2-(3,4-dimethoxyphenyl)ethyl-1-phenyl-2-(phenylsulfinyl)-ethylformamide (6b) using the Pummerer reaction as a key step, respectively. The Pummerer reaction of 6a,b under usual conditions using trifluoroacetic anhydride yielded the vinyl sulfides (8a, b), non-cyclized products, as a major product. The cyclization proceeded when boron trifluoride diethyl etherate was used as an additive reagent, thus giving rise to the corresponding cyclized products (7a) and (7b) in moderate yields. We propose that the enhancing effect of the Lewis acid on the cyclization may be attributable to the involvement of a dicationic intermediate, sulfonium-carbenium dication (23).     

Lewis acid-catalyzed rearrangement of multi-substituted arylvinylidenecyclopropanes

An interesting rearrangement of arylvinylidenecyclopropanes having three substituents at the 1- and 2-positions of the corresponding cyclopropane catalyzed by Lewis acids to give 6aH-benzo[c]fluorine derivatives via a double intramolecular Friedel-Crafts reaction or to give an indene derivative via an intramolecular Friedel-Crafts reaction is described.     

Room-temperature Cannizzaro reaction under mild conditions facilitated by magnesium bromide ethyl etherate and triethylamine

[reaction: see text] A room-temperature convenient Cannizzaro reaction prompted by magnesium bromide ethyl etherate and triethylamine is described for smooth conversion of aromatic aldehydes into their respective alcohols and carboxylic acids. The methodology is applicable to both inter- and intramolecular reactions and could be directed to obtain the carboxylic moiety in the form of an acid, an amide, or an ester compound depending on the selected reaction conditions or workup procedure.     

Remarkably mild and efficient intramolecular Friedel-Crafts cyclization catalyzed by In(III)

[structure: see text]. Indium(III) salts were found to be highly effective catalysts for the intramolecular Friedel-Crafts reaction of simple allylic bromides and arenes. In(III) salts appear to be the most general and possess unique halophilic properties as a Lewis acid for this reaction among the catalysts evaluated to date. Deactivated arenes possessing chloride, bromide, and fluoride underwent smooth reaction when activated by InCl3.     

BF3-promoted synthesis of spiroindenyl heterocycles

An easy and straightforward synthesis of spiroindenyl heterocycles by the repeated treatment of boron trifluoride etherate (BF₃-OEt₂) is reported. The overall transformation from ketones 1 to spiro-fused indenes 3 proceeds via Wittig olefination, deconjugation, Grignard addition, and intramolecular electrophilic cyclization in moderate yields. It presents a novel rearrangement reaction catalyzed by boron trifluoride etherate and broadens the scope of application.     

Radical polymerization of di-n-butyl itaconate in the presence of Lewis acids

Intramolecular chain-transfer reaction takes place in polymerizations of itaconates at high temperatures and/or at low monomer concentrations. Polymerizations of di-n-butyl itaconate (DBI) were carried out at 60 °C in the presence of Lewis acids such as scandium trifluoromethansulfonate. Lewis acids hardly influenced the intramolecular chain-transfer reaction in bulk polymerizations. Polymerizations in methanol accompanied transesterification reaction catalyzed by Lewis acids. In polymerizations in toluene, catalytic amounts of Lewis acids were found to be effective in suppressing the intramolecular chain-transfer reaction. Lewis acids showed no significant influences on stereospecificity of polymerization, though isotactic-specificity increase in polymerizations of other acrylate monomers such as methyl methacrylate.     

BF3·OEt2-promoted reaction of isocyanides with o-aminobenzophenones

Aliphatic isocyanides react with o-aminobenzophenones in dichloromethane under Lewis acid catalysis at ambient temperature to give, unexpectedly, 4-aryl-4-hydroxy-3,4-dihydroquinazolines in good to excellent yields. The outcome of the reaction is rationalized by a skeletal rearrangement of the initially formed ‘intramolecular Passerini’ reaction products, 2-amino-3-hydroxy-3-aryl-3H-indoles.