Highly stereocontrolled synthesis of fluorinated 2,6-trans dihydropyrans via Prins cyclization

A highly efficient method for the synthesis of fluorinated 2,6-trans dihydropyrans via BF₃·Et₂O-promoted Prins cyclization of allenic alcohols and aldehydes is developed. Various 2,6-trans fluorodihydropyrans are obtained in moderate to good yields with excellent diastereoselectivities.     

Arylation of lawsone through BF3-mediated coupling of its phenyliodonium ylide with activated arenes and aromatic aldehydes

Phenyliodonium ylide of lawsone, activated by BF₃·Et₂O, reacts with electron-rich arenes to afford the corresponding 2-aryl-3-hydroxy-1,4-naphthoquinones, in a coupling reaction without metal catalysts. The same type of products, in greater variety and higher yields, are obtained from the reaction of the BF₃·Et₂O-activated ylide with aromatic aldehydes in a synthetically and mechanistically interesting deformylation reaction.     

1,3:4,6-Di-O-benzylidene-d-mannitol as a source for novel chiral intermediates through regioselective reductive cleavage

Synthetically useful chiral intermediates have been synthesized starting from 1,3:4,6-di-O-benzylidene-d-mannitol by regioselective reductive cleavage using BF₃·Et₂O and Et₃SiH in high yields.     

Fluoroaziridines as novel substrates in the modified Petasis reaction: synthesis of monofluorinated propargyl amines

Reaction of 2-fluoroaziridines with potassium alkynyltrifluoroborates in the presence of BF₃·OEt₂ leads to fluorinated propargyl amines in moderate to good yields. The reaction proceeds as an in situ isomerization of 2-fluoroaziridines to α-fluorinated imines, followed by the reaction of the imine with alkynyldifluoroborane, which is generated in situ from the potassium alkynyltrifluoroborates and BF₃·OEt₂.     

BF3·Et2O-induced Beckmann rearrangement of 23-hydroxyiminosapogenins. A shortcut to bisnorcholanic lactones

Treatment of 23-hydroxyiminosapogenins with BF₃·Et₂O in acetic acid produced good yields of the corresponding bisnorcholanic lactones as the sole products.     

Ring opening of 2-phenylazetidines with allylsilanes

N-Activated 2-phenylazetidines were opened regioselectively at the benzylic carbon with various allylsilanes or propargylsilane in the presence of BF₃·Et₂O, providing amino olefins, precursors of biomolecules such as phenyl-homo-kainoids.     

A facile synthesis of (tert-alkoxy)amines

Tertiary alcohols react with stoichiometric BF₃·Et₂O and N-hydroxyphthalimide to yield N-alkoxyphthalimides. Subsequent hydrazinolyses afford the title compounds.     

Barbier allylation-Prins reaction of PEG-bound aldehydes—soluble polymer-supported synthesis of 2,4,6-trisubstituted tetrahydropyrans

PEG-bound aldehydes undergo zinc-mediated Barbier allylation to form homoallylic alcohols, which on further reaction with various aldehydes in the presence of BF₃·Et₂O through a Prins cyclization afford 4-hydroxytetrahydropyrans and 4-fluorotetrahydropyrans.     

An efficient and simple method for synthesis of 2,2-disubstituted-2H-chromenes by condensation of a phenol with a 1,1-disubstituted propargyl alcohol using BF3·Et2O as the catalyst

An efficient and simple method for the synthesis of 2,2-disubstituted-2H-chromenes by one-step cyclocondensation of a phenol with a variety of 1,1-disubstituted propargyl alcohols using BF₃·Et₂O as the catalyst is described.     

Ferrier rearrangement for the synthesis of PEG-bound 2,3-unsaturated glycopyranosyl-amino acids

Amino acid 2,3-unsaturated glycopyranosyls have been prepared by the Ferrier rearrangement of acetyl protected glucals and PEG-bound amino acids in the presence of a catalytic quantity of BF₃·Et₂O in CH₂Cl₂ at ambient temperature.     

Regioselective synthesis of polysubstituted 4H-thiopyrans from β-oxodithioesters

A simple and efficient method for the synthesis of polyfunctionalized 4H-thiopyrans by highly regioselective cyclocondensation of β-oxodithioesters with 1,1,3-trialkyl or aryl substituted prop-2-yn-1-ols using BF₃·Et₂O as the catalyst is described.     

S-tosylsulfenamides,new electrophilic sulfosulfenylating agents

A method has been developed for the synthesis of thiosulfonates by the electrophilic addition of S-tosylsulfenamides to olefins or their electrophilic substitution in aromatic systems. SO₃, Py·SO₃, and BF₃·Et₂O were used as activators. The addition of S-tosylsulfenamides to olefins proceeds through electrophilic trans addition.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2623–2629, November, 1991.     

Lewis acid-catalysed isomerisation of thionolactones to thiolactones: inversion of configuration

Boron trifluoride and indium(III) trifluoromethanesulfonate were found to efficiently catalyse the isomerisation of thionolactones to thiolactones in good yields. When applied to an optically active γ-thionolactone, the isomerisation reaction proceeded with a complete inversion of configuration by using BF₃·Et₂O.     

Synthesis of Novel 1,3,5-Dithiazine Derivatives

The reactions of benzoylacetylene, propiolic acid, and methyl propiolate with 2,4-dithiobiuret and 1-substituted and 1,5-disubstituted 2,4-dithiobiurets in glacial AcOH in the presence of HClO₄ or BF₃·Et₂O were used to obtain 2-substituted 4-amino-6-imino-1,3,5-dithiazinium perchlorates or trifluoroborates, respectively.     

A novel method for tosyloxylation of anilides using phenyliodine bistrifluoroacetate (PIFA)

The direct tosyloxylation of anilides was described in this Letter. In the presence of phenyliodine bis(trifluoroacetate) (PIFA) and BF₃·Et₂O, the reaction of anilides with TsOH provided para-tosyloxylated products with high regioselectivity under mild conditions.     

Chemoselective glycosylation of carboxylic acid with glycosyl ortho-hexynylbenzoates as donors

The gold(I)-catalyzed glycosylation of acid alcohols with glycosyl ortho-hexynylbenzoates in the presence of BF₃·Et₂O and DBU provided the corresponding ester glycosides chemoselectively in high yield; while with DTBP as an additive instead, orthoester formation with the alcohol was effected selectively.     

A one-pot selective deprotective acetylation of benzyl ethers and OTBDMS ethers using the BF3·Et2O-NaI-Ac2O reagent system

An efficient selective deprotection followed by acetylation of several benzyl ethers, including 6-OBn ethers of monosaccharides, and -OTBDMS ethers has been developed by using the BF₃·Et₂O-NaI-Ac₂O reagent system. In addition, both benzylidene and isopropylidene groups are deprotected to form the corresponding diacetates.     

Direct C-3 arylation of N-acetylindoles with anisoles using phenyliodine bis(trifluoroacetate) (PIFA)

The direct C-3 arylation of N-acetylindoles with anisoles was described in this Letter. In the presence of phenyliodine bis(trifluoroacetate) (PIFA) and BF₃·Et₂O, the reaction of N-acetylindoles with anisoles provided C-3 arylindoles with high regioselectivity under mild conditions.     

Electroreductive intramolecular coupling of aliphatic cyclic imides with ketones and O-methyloximes

The electroreductive intramolecular coupling of aliphatic cyclic imides with ketones in isopropanol gave five- and six-membered cyclized products. Similarly, the electroreductive intramolecular coupling of aliphatic cyclic imides with O-methyloximes afforded five-, six-, and seven-membered cyclized products. These reactions provide a useful method to synthesize azabicyclo[n.m.0] compounds. The bicyclic products were stereoselectively transformed to the corresponding deoxylated compounds by reduction with NaB(CN)H₃ or Et₃SiH/BF₃·Et₂O.     

Intramolecular cycloaddition/cycloreversion of (E)-3β,17β-diacetoxy-5,10-secoandrost-1(10)-en-5-one

Treatment of 3β,17β-diacetoxy-5,10-secoandrost-1(10)-en-5-one with BF₃·Et₂O was shown to proceed with cleavage of the macrocycle and formation of a new compound containing a cyclopentenone ring. Based on DFT calculations, an intramolecular Lewis acid promoted [2+2]cycloaddition, followed by a cycloreversion of the intermediate oxetane, is proposed as a possible reaction mechanism.