Use Of BF3 Research Articles

BF3 ⋅ OEt2 and Visible Light‐Controlled [3,3]‐ or [1,3]‐Rearrangement of Quinazolinone N−O Aryl Moieties

AbstractWe described a base‐promoted O‐arylation of N3‐hydroxyl quinazolinones with diaryliodonium salts and sequential BF3 ⋅ OEt2 and visible light‐controlled [3,3]‐ or [1,3]‐rearrangements of quinazolinone N−O aryl moieties to prepare a variety of 2‐(quinazolin‐4‐yloxy)phenols and atropisomeric 3‐(2‐hydroxyphenyl)quinazolin‐4‐ones in 44%‐75% yields and 28%‐70% yields, respectively. Mechanistic studies showed that HBF4 generated in situ from BF3 ⋅ Et2O and water served as the catalyst in this process and aryloxyquinazolinium salts are vital intermediates promoting the [3,3]‐ or [1,3]‐rearrangements. The N−O aryl moieties of aryloxyquinazolinium salts were found to undergo solely [3,3]‐rearrangement with heating whereas [1,3]‐rearrangement occurred via a radical process under irradiation of visible light. This method highlights the formation of aryloxyquinazolinium salts based on the use of BF3 ⋅ OEt2 and visible light to prompt [1,3]‐rearrangement generating atropisomeric quinazolinones.

Palladium‐Catalyzed Oxidative Arylating Carbocyclization of Allenynes: Control of Selectivity and Role of H2O

Highly selective protocols for the carbocyclization/arylation of allenynes using arylboronic acids are reported. Arylated vinylallenes are obtained with the use of BF3⋅Et2O as an additive, whereas addition of water leads to arylated trienes. These conditions provide the respective products with excellent selectivities (generally >97:3) for a range of boronic acids and different allenynes. It has been revealed that water plays a crucial role for the product distribution.

Palladium‐Catalyzed Oxidative Arylating Carbocyclization of Allenynes: Control of Selectivity and Role of H2O

AbstractHighly selective protocols for the carbocyclization/arylation of allenynes using arylboronic acids are reported. Arylated vinylallenes are obtained with the use of BF3⋅Et2O as an additive, whereas addition of water leads to arylated trienes. These conditions provide the respective products with excellent selectivities (generally >97:3) for a range of boronic acids and different allenynes. It has been revealed that water plays a crucial role for the product distribution.

Highly exfoliated nanostructure in trifunctional epoxy/clay nanocomposites using boron trifluoride as initiator

ABSTRACTEpoxy/clay nanocomposites based upon a trifunctional epoxy resin, triglycidyl p‐amino phenol (TGAP), have been prepared by intercalating an initiator of cationic homopolymerization, a boron trifluoride monoethylamine (BF3·MEA) complex, into the montmorillonite clay galleries before the addition of the TGAP and the curing agent, 4,4‐diamino diphenyl sulfone (DDS), and effecting the isothermal curing reaction. The BF3·MEA enhances the intragallery cationic homopolymerization reaction, which occurs before the extragallery cross‐linking reaction of the TGAP with the DDS, and which hence contributes positively to the mechanism of exfoliation of the clay. The effects of isothermal cure temperature and of BF3·MEA content have been studied, in respect of both the reaction kinetics, monitored by differential scanning calorimetry, and the nanostructure, as identified by small‐angle X‐ray scattering and transmission electron microscopy. It is shown that the use of BF3·MEA in this way as an initiator of intragallery homopolymerization significantly improves the degree of exfoliation in the cured nanocomposites. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014, 131, 40020.

Multicomponent synthesis and anticonvulsant activity of monocyclic 2,6-diketopiperazine derivatives

In this study, a series of diastereomerically pure monocyclic 2,6-diketopiperazine (2,6-DKP) derivatives were synthesized. The key synthetic step involved a multicomponent Ugi five-center, four-component reaction which was used to generate the convertible tert-butylamidoesters with both good yields and high diastereoselectivity toward the desired bioactive (S,S) absolute configuration. In subsequent steps, selective tertbutyl cleavage by use of BF3·CH3COOH and base-induced intramolecular cyclocondensation gave the final 2,6-DKP derivatives. The relative stereochemistry of the target molecules was confirmed by 1H NMR experiments. The compounds obtained were submitted to in vivo screening in animal models of epilepsy. Some of them displayed good activity in maximal electroshock seizure and 6 Hz tests.

Synthesis of the AB‐Ring Pyranolactone Substructure of Granaticin A

AbstractA synthesis of the AB‐ring substructure of granaticin A was developed. The pyranolactone moiety was stereoselectively accessed by Sharpless asymmetric dihydroxylation and subsequent oxa‐Pictet–Spengler cyclization. The use of BF3·OEt2 resulted in the formation of the cis pyranolactone, whereas the combination of BF3·OEt2 with trifluoroacetic acid led to the trans isomer. The resulting hydroquinones were cleaved selectively by ozonolysis to dicarboxylic acids. An aryl Grignard reagent could be regioselectively added to unsymmetrical anhydrides. As an alternative strategy for the construction of the B‐ring, a benzyne–furan cycloaddition could be established.

ChemInform Abstract: Chemoselective Allylation of Aldimine with Allyltriethylgermane by the Combined Use of BF3×OEt2 and AcOH.

Allyltriethylgermane reacts with aldimines in preference to aldehydes by means of BF3•OEt2 and AcOH to afford homoallylic amines in high yields; three component syntheses of homoallytic amines starting from aldehyde, aniline and allylgermane were successfully achieved.

Diels–Alder Cycloadditions of 5‐Hydroxy‐2‐pyrones: 2H‐Pyran‐2,5‐diones and 5‐(tert‐Butyldimethylsilyloxy)‐2‐pyrones as Synthons

AbstractDiels–Alder (DA) cycloadditions of 5‐hydroxy‐2‐pyrones based on the use of 2H‐pyran‐2,5‐diones and 5‐(tert‐butyldimethylsilyloxy)‐2‐pyrones as synthons have been developed. Upon treatment either with a base or with a Lewis acid, 2H‐pyran‐2,5‐diones equilibrated to 5‐hydroxy‐2‐pyrones and underwent DA cycloaddition. The base‐catalyzed protocol was optimized with cHex2NMe (0.1 equiv.) in tBuOH at room temperature, which gave the bicyclic cycloadducts in yields of up to 81 % (endo/exo = 6.2:1). The Lewis‐acid‐promoted protocol was optimized by conversion of 2H‐pyran‐2,5‐diones into 5‐(tert‐butyldimethylsilyloxy)‐2‐pyrones and use of BF3·OEt2, which afforded the same DA products in yields of up to 90 % (endo/exo = 12:1).

Lewis Acid Catalyzed Diels−Alder Reactions of 1,2-Naphthoquinones

The use of BF(3) x OEt(2) catalysis in Diels-Alder reactions of 3,4-unsubstituted 1,2-naphthoquinones provides direct access to cis-tetrahydrophenanthrene derivatives in good to excellent yields (66-99%) without rapid adduct aromatization commonly associated with corresponding thermal processes.

A New Approach to Promoting Sluggish Diels−Alder Reactions: Dihapto-Coordination of the Diene

The cycloaddition between 1,3-cyclohexadiene and various enones and enals (methyl vinyl ketone, ethyl vinyl ketone, methacrolien) is accomplished at room temperature in yields ranging from 51 to 68% without the use of Lewis acids, high pressures, or microwave reactors. This normally sluggish cyclization is accomplished by precoordination of the diene to a pi-basic molybdenum complex. The eta2-bound metal is thought to promote a Michael reaction between the uncoordinated portion of the diene and the enone, and the resulting enolate then closes to form the cycloalkene product. The organic cycloadduct is removed by oxidation with air or with silver triflate in nearly quantitative yield. For more sterically hindered enones (e.g., mesityl oxide) and for methyl acrylate, the desired outcome requires the use of BF3.OEt2, and yields are significantly lower (15-35%)

Probing the basicity of regular and defect sites of alkaline earth metal oxide surfaces by BF3 adsorption: a theoretical analysis.

The basicity of regular and low-coordinate (LC) sites (steps, edges and corners) at the surface of alkaline earths with NaCl structure (MgO, CaO, SrO, and BaO) has been investigated by using BF3 as a probe molecule. B-O and B-F distances; O-B-F bond angles; B-F asymmetric stretching frequencies; O, B and F 1s core-level binding energies; and the interaction energy of adsorbed BF3 were determined by means of DFT calculations on cluster models. These adsorption properties were compared with those of complexes of BF3 with molecules with various basicities (water, ammonia, phosphine, etc.). We show that many properties of adsorbed BF3, and in particular the experimentally accessible shifts in vibrational frequency, in B and F 1s core levels, and in BF3 desorption temperature, exhibit a linear correlation with the surface basicity as measured by the vertical ionization potential of the oxide anions. On the other hand, shifts of the O 1s core level binding energy do not provide a simple way to detect surface basicity. On a given oxide surface, the differing basicities of various sites result in measurable differences in adsorption properties. This suggests the potential use of BF3 as a probe molecule for titrating LC sites on the surface of ionic oxides.

New transformations of 2-nitro-2,3-dihydrofurans to multi-functionalized dihydrofurans

A new type of transformation of 2-nitro-3-substituted-dihydrofurans to 4-formyl-2-hydroxy-3-substituted-2,3-dihydrofurans was accomplished in 63–84% yields by use of BF3·OEt2 in CH2Cl2 at −78 to 0°C.

BF3 Adsorption on α-Cr2O3 (101̄2): Probing the Lewis Basicity of Surface Oxygen Anions

Acid/base characterizations of metal oxide surfaces are used often to explain their catalytic behavior. BF3, a strong Lewis acid, is used in this investigation as a probe molecule to interrogate the basicity of well-defined Cr2O3 (101̄2) surfaces. BF3 clearly probes differences in oxide ions of different coordination on Cr2O3 (101̄2). The heat of adsorption of BF3 shows that terminal chromyl oxygens are stronger Lewis bases than three-coordinate oxygen anions on the nearly stoichiometric surface. The trends in basicity found with BF3 are the opposite of those found from the heat of adsorption of CO2, a common probe molecule used to investigate the basicity of oxide surfaces. The use of BF3 as a probe molecule is complicated by some dissociation and the slow build up of surface boron and fluorine during consecutive thermal desorption runs.

Chemoselective allylation of aldimine with allyltriethylgermane by the combined use of BF3•OEt2 and AcOH

Allyltriethylgermane reacts with aldimines in preference to aldehydes by means of BF3•OEt2 and AcOH to afford homoallylic amines in high yields; three component syntheses of homoallytic amines starting from aldehyde, aniline and allylgermane were successfully achieved.

Novel Lewis Acid Promoted Reactions of Allylsilane Bearing Bulky Silyl Substituents and Aldehydes

Abstract Reported herein are two novel modes of reactions that were mediated by the proper choice of Lewis acid. Thus, by the influence of SnCl4, allyl-t-butyldimethylsilane reacted with aldehyde in 2:1 stoichiometry to afford a ketone derivative. In contrast, use of BF3•OEt2 led to the formation of a 1,3-dioxane derivative, which is a 1:2 adduct.

ChemInform Abstract: The Use of BF3×Et2O in the Synthesis of Fluorinated Anthracyclinones.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Additions of Silyl Enol Ethers to β‐Formyl Esters – a Chelate‐controlled Synthesis of the Pheromone (+)‐Eldanolide

AbstractChelate‐controlled Mukaiyama reaction of silyl enol ethers 2a, 2b, 2c, and 2d with β‐formylcarboxylate 1 in the presence of TiCl4 provided γ‐lactones 3a, 3b, 3c, and 3d in very good yields and with good to excellent trans selectivities. The use of BF3, SnCl4, and SnBr4 as Lewis acids afforded 3a with moderate cis selectivity thus excluding chelate control. Starting with (S)‐1 TiCl4‐promoted reaction with 2b, we obtained optically active γ‐lactone 3b which was efficiently converted into the pheromone (+)‐eldanolide in two steps. The enantiomeric excess of 87% proved that the sequence proceeds without detectable racemization.

Comparison of six methylation methods for analysis of the fatty acid composition of albacore lipid

SummarySix methods widely used to produce methyl esters for the gas chromatographic determination of the fatty acid composition of a marine lipid were compared. Four acid‐catalyzed methods (1% H2SO4: CH3OH; 5% HCl: CH3OH; 7% and 14% BF3: CH3OH) and two base‐catalyzed methods [0.5M NaOCH3: CH3OH; (1:4) tetramethylguanidine: CH3OH] were used.The use of BF3: CH3OH (7% and 14%) gave a lower content of 18:1 n9 than the other methods and produced an artefact (2.7–3.2% of total fatty acid content) eluting between the 20:5 and 24:1 fatty acid methyl esters. No significant differences were obtained between the other four methods.Accordingly the use of BF3: CH3OH for transmethylation of marine lipids is not recommended. Results obtained in the other four methods showed that all are comparable.

Cationic copolymerization of tetrahydrofuran with epoxides. I. Polymerization mechanism in the presence of a glycol

AbstractPolymerization of several epoxides and their copolymerization with tetrahydrofuran have been studied. The polymerizations were carried out by use of BF3·O(C2H5)2 as catalyst in the presence of 1,4‐butanediol. Variations of catalyst and 1,4‐butanediol ratio and concentration affect polymerization rate, molecular weight, and the formation of cyclic oligomers. The latter is also influenced by monomer fed ratio in the case of the copolymerizations. These effects are discussed, and some observations are made concerning the mechanism, particularly with respect to the role of the 1,4‐butanediol. Mayo‐Lewis monomer reactivity ratios were determined. The ratios found differed from previously published figures.

New Data on Isotopes

ISOTOPIC WEIGHTS BY THE DOUBLET METHOD CONTINUING work with ray new mass-spectrograph1, I have made measurements of several more doublets. That of N, CH2 was easy to obtain with a mixture of nitrogen and methane, and gave very consistent results. The vapour of pure heavy water did not, at first, give as strong a line at 20, OD2, as was hoped, but as 19, ODH, was good, CF4 was introduced and the doublet F, ODH measured. Later the intensity of OD2 was improved and enabled a comparison with 20Ne to be made. The latter line was then coupled with doubly charged 40A, giving a very close doublet. By the use of BF3 with a suitable quantity of neon, the fairly wide doublet 10B, 20Ne + + was photographed. The spectra also showed the expected doublet at 29 due to 29Si and 10BF. This gave the first accurate measurement of the mass of the former. The following are the results: