Stanna-Brook rearrangement of carboxylic acid derivatives. Synthetic utility and mechanistic studies

[reaction: see text] The reaction of R(3)SnLi with carboxylic acid derivatives proceeds through a novel, very fast stanna-Brook rearrangement that generates alpha-alkoxyorganolithium compounds as intermediates. The outcome of these reactions depends on the nature of the carboxyl derivatives. Reaction of R(3)SnLi with ester derivatives gives rise to coupled products through a novel C-C bond formation reaction. Experimental evidence of the detailed reaction mechanism is provided.     

Donor-acceptor complexes of quinoline N-oxides with boron trifluoride

Molecular n-v complexes of quinoline N-oxides with BF₃ have been studied by electronic and IR spectroscopy. In most case the donor centre is the oxygen atom of the N-oxide group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1087–1092, August, 1994.     

Favorski type rearrangement in the lead tetraacetate oxidation of enamines promoted by boron trifluoride

Favorski type rearrangement has been achieved in the lead tetraacetate oxidation of enamines in the presence of boron trifluoride etherate and alcohol.     

Facile rearrangement of O-silylated oximes on reduction with boron trifluoride/borane

[reaction: see text] Aromatic O-triisopropylsilyl ketoximes were efficiently rearranged to cyclic and acyclic aniline derivatives on reduction with BF3-ethearate/borane. The bulk of the substituents on the silicon atom, the size of the aliphatic ring, and the presence of alkoxy substituents on the aryl group all play an important role in the aniline.     

Large gas-solid structural differences in complexes of haloacetonitriles with boron trifluoride

The structural properties of the singly halogenated derivatives of CH(3)CN-BF(3) (X-CH(2)CN-BF(3): X = F, Cl, Br, I) have been investigated via single-crystal X-ray crystallography, solid-state infrared spectroscopy, and correlated electronic-structure theory. Taken together, these data illustrate large differences between the gas-phase and solid-state structures of these systems. Calculated gas-phase structures (B3PW91/aug-cc-pVTZ) of FCH(2)CN-BF(3), ClCH(2)CN-BF(3), and BrCH(2)CN-BF(3) indicate that the B-N dative bonds in these systems are quite weak, with distances of 2.422, 2.374, and 2.341 A, respectively. However, these distances, as well as other calculated structural parameters and normal-mode vibrational frequencies, indicate that the dative interactions do become slightly stronger in proceeding from F- to Br-CH(2)CN-BF(3). In contrast, solid-state structures for FCH(2)CN-BF(3), ClCH(2)CN-BF(3), and ICH(2)CN-BF(3) from X-ray crystallography all have B-N distances that are quite short, about 1.65 A. Thus, the B-N distances of the F- and Cl-containing derivatives contract by over 0.7 A upon crystallization. Large shifts in the vibrational modes involving motions of the BF(3) subunit parallel these structural changes. An X-ray crystal structure could not be determined for BrCH(2)CN-BF(3)(s), but the solid-state IR spectrum is consistent with those obtained previously for related complexes and suggests that the solid-state structure resembles those of the others, and in turn, implicates a large gas-solid structural difference for this species as well.     

Thermal stability of epoxy compounds cured with boron trifluoride complexes

The thermal resistances of epoxy resins cured with complexes of boron trifluoride with benzylamine, 2-benzylaminoethanol and 2-anilinoethanol were examined. Thermal analysis data were used to compare the thermal resistances of epoxy compusitions cured with polyamines (aliphatic and aromatic), acid anhydrides and complexes of boron trifluoride with the above amines.

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Zusammenfassung Der WÄrmewiderstand von mit Komplexen von Bortrifluorid mit Benzylamin, 2-Benzylamino-Äthanol und 2-Anilino-Äthanol gehÄrteten Epoxyharzen wurde untersucht. Anhand thermoanalytischer Daten wurden die WÄrmewiderstandswerte von mit (aliphatischen und aromatischen) Polyaminen, SÄureanhydriden und Komplexen von Bortrifluorid mit den oben angeführten Aminen gehÄrteten Epoxy-Kompositionen miteinander verglichen.

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Stereochemical course of the hydrogen migration in the boron trifluoride etherate-catalyzed rearrangement of 1,1-disubstituted epoxides

Mechanistic studies on the BF₃·Et₂O-catalyzed rearrangement of optically active, regioselectively deuterated 1,1-disubstituted epoxides to aldehydic products revealed that the two hydrogens migrate at the migration terminus with opposite stereochemical preferences, i.e. the hydrogen anti to the bulky substituent prefers to migrate with inversion of configuration, whereas the hydrogen syn to the bulky substituent prefers to migrate with retention of configuration.     

Donor-acceptor complexes of dipyrrolylmethenes with boron trifluoride as intermediates in the synthesis of Bodipy

The formation of donor-acceptor complexes of dipyrrolylmethene and structurally similar biladiene-a,c with boron trifluoride was studied by electronic absorption, IR, and ¹H NMR spectroscopies as well as by quantum chemical calculations. It was shown that the formation of donor-acceptor complexes is the first step of the synthesis of the corresponding boron fluoride chelate complexes (Bodipy). The hydrogen bond N—H...F—B additionaly stabilizes the donor-acceptor complexes. The stability constants, geometric parameters, and energy characteristics of the donoracceptor complexes were determined; the two-step mechanism of Bodipy synthesis was analyzed.     

A novel boron trifluoride etherate mediated deep-seated rearrangement of an α,β-epoxyketone

Acid catalysed reaction of carvone epoxide 2 resulted in dimeric products 3 and 4, in contrast to the expected ring contraction product. Reaction of β-methylcarvone epoxides 8 and 11 with acids furnished 2-acetyl-4-isopropenylcyclopentanones 9 and 14 containing a stereodefined quaternary carbon atom. On the other hand, the reaction of epoxides 8 and 11 with boron trifluoride etherate lacks the stereoselectivity and in addition, anti-epoxide 8 furnished lactone 18 via an unusual deep seated rearrangement.     

Addition of boron trifluoride complexes of organocopper reagentsto aldimines containing α-hydrogens

RCu · BF₃, generated $\text{in situ}$ from Grignard reagents, CuI, and BF₃ · OEt₂, added to aldimines containing α-hydrogens to afford secondary amines in good yields. Boron trifluoride complex of dialkylcuprate gave essentially the same result with wider application.     

An ab initio and cryospectroscopic study of the hydrogen chloride and boron trifluoride complexes of cyclopropene

Mid-infrared spectra of cyclopropene (c-C3H4) mixtures with HCl or BF3, dissolved in liquefied argon and in liquefied nitrogen have been examined. Evidence was found for the formation of two different isomers of the 1:1 complexes: a pi-type complex in which the interaction occurs with the pi-bond of cyclopropene, and a sigma-type complex in which the electron acceptors interact with one of the CC single bonds. At lower temperatures, indications for the formation of a 1:2 chain-type complex were found. Using spectra recorded between 90 and 124 K in liquid argon, the complexation enthalpies for the pi- and sigma-complexes with HCl were determined to be -8.8(3) and -7.9(3) kJ mol-1, respectively. For the pi-complex with BF3 a value of -7.4(3)kJ mol-1 was found. Structural and spectral information on the 1:1 complexes was obtained from B3LYP/6-311++G(d,p) and MP2(FC)/6-31+G(d) calculations. Using Free Energy Perturbation Monte Carlo simulations to calculate the solvent influences, and statistical thermodynamics to account for zero-point vibrational and thermal contributions, the solution enthalpies were transformed into complexation energies with values of -15.5(6) and -13.8(8) kJ mol-1 for the pi- and sigma-isomers of c-C3H4.HCl, respectively, and of -12.7(8) kJ mol-1 for the pi-type BF3 complex.     

Donor-acceptor complexes of linear oligopyrroles with boron trifluoride. Spectral studies and quantum-chemical simulation

Intermediate products of synthesis of the boron trifluoride complexes with linear oligopyrroles are found. By means of electronic spectroscopy it was shown that the reaction of linear oligopyrroles with boron trifluoride in solutions resulted in the formation of stable donor-acceptor complexes. Their composition was established and the formation constants were evaluated. It was shown that transformation of these complexes in the corresponding borofluoride complexes is possible only while boiling the reaction mixture. By means of quantum-chemical methods the structural and energy parameters of the donor-acceptor complexes under study were calculated.     

Fries reaction and dakin rearrangement in benzo-2,1,3-thiadiazoles

The Fries rearrangement of 4- and 5-acetoxybenzo-2,1,3-thiadiazoles has given 4-hydroxy-7-acetyl- and 5-hydroxy-4-acetylbenzo-2,1,3-thiadiazoles, which on oxidation afford mixtures of 5-chloro-4,7-dioxo- and 5,6-dichloro-4,7-dioxobenzo-2,1,3-thiadiazole and of 6-chloro-4,5-dioxo- and 6,7-dichloro-4,5-dioxobenzo-2,1,3-thiadiazole. Reaction of 6,7-dichloro-4,5-dioxobenzo-2,1,3-thiadizole with ortho-phenyl-enediamine gives 4,5-dichloro-2,1,3-thiadiazolo[4,5-a]phenazine.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1683–1687, December, 1987.     

The vibrational spectra of the boron halides and their molecular complexes. Part 13. Ab initio studies of the complexes of boron trifluoride with formaldehyde and some of its analogs

The structure, the interaction energy, and the vibrational spectrum of the electron donor–acceptor complex formed between boron trifluoride, as a Lewis acid, and formaldehyde, as a Lewis base, have been determined by means of ab initio calculations at the second‐order level of Møller–Plesset perturbation theory, using a triple‐zeta basis set with polarization and diffuse functions on all atoms. The object was to examine the differences in the properties of the complexes formed between boron trifluoride and an oxygen base containing oxygen in the sp² hybrid state with those of some sp³ oxygen bases studied earlier. The investigation has then been extended to include the related bases thioformaldehyde and methanimine, to assess the effect of substituting the oxygen atom by a sulphur atom or an imino group. A further range of formaldehyde analogs, containing one and two methyl groups, one and two fluorine atoms, and one methyl group and one fluorine atom, has also been included. The preferred structure of each complex has been identified. The computed data have been compared, and the complex properties correlated with some relevant physical properties of the bases. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

The vibrational spectra of the boron halides and their molecular complexes Part 10. The complexes of boron trifluoride with ammonia and its methyl derivatives. An ab initio study

Ab initio calculations, at the level of second order M?ller-Plesset perturbation theory, and using a triple-zeta Gaussian basis set with polarization and diffuse functions on all atoms, have been carried out on the donor-acceptor complexes of boron trifluoride with ammonia and its mono-, di- and trimethyl derivatives. The structures, interaction energies and vibrational spectra of the complexes have been determined. An eclipsed and a staggered conformer have been examined for each complex, and the preferred conformer was found to be the staggered species in each case. The computed data have been compared with those for some similar complexes containing boron trifluoride and a series of oxygen and sulphur electron donors (water, hydrogen sulphide, methanol, methanethiol, dimethyl ether and dimethyl sulphide) and the effect of successive methyl substitution in all three series has been investigated.     

A mechanistic study of the alkaline hydrolysis of diaryl sulfate diesters

Nearly all of the reported studies of reactions of sulfate diesters are for dialkyl or alkyl aryl diesters, which undergo reaction by carbon-oxygen bond fission. Sulfuryl transfer reactions of sulfate diesters (RO-SO(2)-OR') proceeding by attack at sulfur have been little explored. When both ester groups are aryl groups the hydrolysis reaction (sulfuryl transfer to water) occurs by way of attack at sulfur. The alkaline hydrolysis of diaryl sulfate diesters was shown to obey first-order kinetics with respect to [(-)OH] and proceed through S-O bond fission, in a mechanism that is most likely concerted. Activation parameters for 4-chloro-3-nitrophenyl phenyl sulfate and 4-nitrophenyl phenyl sulfate gave the following respective values: Delta H(++) = 88.0 +/- 0.1 and 84.83 +/- 0.06 kJ mol(-)(1) and Delta S(++) = -37 +/- 1 and -50.2 +/- 0.5 J mol(-)(1) deg(-)(1). The dependence of the second-order rate constant for hydrolysis on leaving group pK(a) was analyzed giving a beta(lg) slope of -0.7 +/- 0.2 and a Leffler alpha parameter value of 0.36. A (15)k kinetic isotope effect (KIE) for the hydroxide attack on 4-nitrophenyl phenyl sulfate of 1.0000 +/-0.0005 and an (18)k(lg) KIE value of 1.003+/-0.002 were obtained.