Dibromo Derivatives Research Articles

4,7-Dibromo-substituted 2,1,3-benzothia(selena,oxa)diazoles and [1, 2, 5]thia(selena)diazolo[3,4-c]pyridines as building blocks in solar cells components (microreview)

2,1,3-Benzothia(selena,oxa)diazoles and [1, 2, 5]thia(selena)diazolo[3,4-c]pyridines are important building blocks in dye-sensitized solar cells. This microreview summarizes synthesis of their dibromo derivatives and conversion to dye-sensitized solar cell components by cross-coupling reactions and copolymerization.

Unsymmetrical Bipyrrole‐Derived β‐Tetraalkylporphycenes and C–H···Br–C Interaction Induced 2D Arrays of the 2:1 Supramolecular Sandwich Complex of Their cis‐/trans‐Dibromo Isomers

Two novel stable β‐tetraethylporphycenes (TEPos), namely, trans‐TEPo (1T) and its unsymmetrical isomer cis‐TEPo (1C), were synthesized by reductive McMurry coupling of an unsymmetrical bipyrrole dialdehyde and were isolated through recrystallization. Both isomers showed interesting photophysical properties. Their corresponding dibromo derivatives obtained through bromination of a mixture of 1C and 1T, however, could not be separated in pure form. Interestingly, they were found to form an unprecedented 2:1 supramolecular sandwich complex through π–π stacking interactions, and in addition, only strong C–H···Br–C interactions among the oppositely oriented cis isomers led to the formation of 2D arrays in the solid state.

Synthesis of polyfunctional phosphorus-containing calixarenes in cycloaddition reactions of azides to alkynes

Mono- and dibromo derivatives of calix[4]arene were used for the first time in phosphorylation, alkylation, and azide-alkyne cycloaddition sequence in order to synthesize polyfunctional macrocycles containing phosphine oxide groups at the upper rim and 1,4-disubstituted triazole rings at the lower rim. The effect of reaction conditions onto the selectivity of the lower-rim alkylation of phosphoruscontaining calixarenes and the ratio of spatial isomers in the exaustively alkylated products was studied. The reduction of phosphine oxide groups and modification of functional groups in the triazole rings were used for the synthesis of bulky hydrophilic phosphinecontaining ligands. The catalytic activity of in situ obtained rhodium complexes of phosphine-containing calixarenes was preliminarily studied by 1-octene hydroformylation in ethanol.

Designing, synthesis, and antimicrobial action of oxazoline and thiazoline derivatives of fatty acid esters

In this study, a novel series of oxazoline and thiazoline were designed as inhibitors of cytochrome P450 14 alpha-sterol demethylase (CYP51) from Candida albicans and peptide deformylase (PDF) of Escherichia coli. The long chain dibromo derivative of fatty acid esters on reaction with urea and thiourea gave their corresponding oxazolines and thiazolines, respectively. All the compounds were characterized by their spectral data (IR, 1H NMR, 13C NMR and MS) and tested for antibacterial and antifungal activity by disk diffusion assay and minimum inhibitory concentration by the broth microdilution method against gram-positive and gram-negative strains of bacteria as well as fungus strains. The investigation into antimicrobial screening revealed that all the compounds were found to be potent antimicrobial agents. After calculating likeness drug properties of the compounds by Prediction of Activity Spectra for Substances software, ADMET-related descriptors were computed to predict the pharmacokinetic properties for the active and bioavailable compounds by discovery studio 2.5. Molecular docking studies have been performed on PDF of E. coli and CYP 450-14DM of C. albicans to understand the mode of binding of the molecules in the active site of the receptor. Compounds (2-amino-5-(carbomethoxyoctyl)-1,3-oxazoline, 2-amino-5-(carbomethoxyoctyl)-1,3-thiazoline and 2-amino-4-pentyl-5-[(8’R)-8’ hydroxy (carbomethoxydecyl)-1,3-oxazoline) showed excellent antimicrobial activity nearly equivalent to the control compounds and compounds, 2-amino-4-octyl-5-(carbomethoxyheptyl)-1,3-oxazolin, 2-amino-4-(2’R)(2’-hydroxy octyl)-5-(carbomethoxyheptyl)-1,3-oxazoline and 2-amino-4-pentyl-5-[(8’R)-8’-hydroxy(carbomethoxy decyl)-1,3-oxazolineshowed vasodilation and antihypertensive properties. Furthermore, a computational analysis of physicochemical parameters revealed that the most of the compounds possessed drug-like attributes. Using Bioinformatics approach, we found a correlation between the observed and predicted antimicrobial activities.

A novel synthesis of halogenated oxa[9]helicenes and dibromo spiro-lactone derivative by the reaction of helical quinones with halogenating regents

A new class of halogenated oxa[9]helicene derivatives along with dibromo spiro-lactone were synthesized in excellent yields, and the compounds were successfully characterized by different spectroscopic techniques (e.g. 1H and 13C NMR, HRMS spectroscopy and X-ray crystallography).

ChemInform Abstract: Chiral Hexahalogenated 4,4′‐Bipyridines.

The preparation of 27 isomers of chiral hexahalogeno-4,4′-bipyridines by means of two complementary methods is described. The first one is convergent and based on the LDA-induced 4,4′-dimerization of trihalopyridines, whereas the second method is divergent and achieved through regioselective halogenation reactions of 4,4′-bipyridine-2,2′-diones. Iodine in 2,2′-positions of the 4,4′-bipyridines was introduced by a copper-catalyzed Finkelstein reaction (Buchwald procedure) performed on 2,2′-dibromo derivatives. Selected compounds of this new family of atropisomeric 4,4′-bipyridines were enantioseparated by high performance liquid chromatography on chiral stationary phases, and the absolute configurations of the separated enantiomers were assigned by using X-ray diffraction analysis. The latter revealed that various halogen bond types are responsible for crystal cohesion.

Structural analysis and antitumor potential of novel 5,6-disubstituted-17a-homo-17-oxa-androstane derivatives

Starting from 3β-acetoxy-17a-homo-17-oxa-androst-5-en-16-one (1) and in the reaction with N-bromoacetamide (NBA) and perchloric acid, the 5α-bromo-6β-hydroxy (2), 5β,6β-epoxy (3) and 5α,6β-dibromo (4) derivatives were obtained. The structure of compounds 2–4, particularly stereochemistry at C5 and C6, is established by detailed NMR and X-ray analysis. The in vitro antiproliferative activity of newly synthesized compounds 2–4 against six human tumor cell lines was evaluated. All three compounds showed a significant toxicity toward hormone-independent breast adenocarcinoma MDA-MB-231 and cervical carcinoma cells HeLa, while dibromo derivative 4 was active toward five human cancer cell lines. These new 5,6-disubstituted-D-homolactone steroidal compounds have also displayed selectivity toward cancerous cell lines against inactivity found for noncancerous control cell line. This selectivity was not found for control compound, well-known chemotherapy drug cisplatin.

Chiral Hexahalogenated 4,4'-Bipyridines.

The preparation of 27 isomers of chiral hexahalogeno-4,4'-bipyridines by means of two complementary methods is described. The first one is convergent and based on the LDA-induced 4,4'-dimerization of trihalopyridines, whereas the second method is divergent and achieved through regioselective halogenation reactions of 4,4'-bipyridine-2,2'-diones. Iodine in 2,2'-positions of the 4,4'-bipyridines was introduced by a copper-catalyzed Finkelstein reaction (Buchwald procedure) performed on 2,2'-dibromo derivatives. Selected compounds of this new family of atropisomeric 4,4'-bipyridines were enantioseparated by high performance liquid chromatography on chiral stationary phases, and the absolute configurations of the separated enantiomers were assigned by using X-ray diffraction analysis. The latter revealed that various halogen bond types are responsible for crystal cohesion.

Dibromohydantoins as halogen bond (XB) donors: a route toward the introduction of chirality in halogen bonded systems

N,N′-Dibromohydantoins, known as electrophilic bromination reagents, are successfully used here as halogen bond (XB) donors, as demonstrated in their crystalline adducts with para-substituted pyridines acting as halogen bond acceptors. 1 : 1 adducts of the achiral 5,5-dimethyl-N,N′-dibromohydantoin (DBH) are crystallized with methylisonicotinate, 4-trifluoromethylpyridine and 4-cyanopyridine, while both nitrogen atoms of pyrazine are engaged in halogen bonding in the 2 : 1 adduct (DBH)2·(pyrazine). A strengthening of the XB interaction between the imidic N–Br group of DBH and the pyridinic nitrogen atom is observed with the more electron rich pyridines in the order Py–CO2Me > Py–CF3 > Py–CN > pyrazine. Chiral hydantoins and their N,N′-dibromo derivatives are obtained in good yields from different amino acids (phenylglycine, phenylalanine, valine and leucine). The ability of such enantiopure N-iodoimide derivatives to act as halogen-bond donors is demonstrated in the 1 : 1 methylisonicotinate adduct with (S)-5-isobutyl-N,N′-dibromohydantoin.

Synthesis of enantiopure 2,4,8,10-tetrasubstituted Tröger base derivatives

Chiral tetramethyl and dibromo-dimethyl substituted Tröger base derivatives are readily prepared in enantiomerically pure forms using camphor sulfonic acid as a resolving agent. The (S,S)-isomers of these derivatives were obtained with 95–99% ee by precipitation using (1S)-(+)-10-camphor sulfonic acid and the partially resolved samples present in the mother liquor were enriched by treatment with (1R)-(−)-10-camphor sulfonic acid to obtain the (R,R)-isomers of tetrasubstituted Tröger base derivatives with 96–99% ee. In the case of 2,8-dibromo-4,10-dimethyl derivative, the (R,R)-isomer was obtained with 96–97% ee from the filtrate fraction after the (S,S)-enantiomer precipitated out. The dibromo derivative is readily functionalized to access a new chiral amine system containing a chiral phenylethylamine moiety.

Absolute configuration of labdane diterpenoids from Physalis nicandroides.

A mixture of the new epimeric labdenetriols 1 and 2 was isolated from the aerial parts of Physalis nicandroides. The structures of 1 and 2, including their absolute configurations, were established by analyses of their spectroscopic data, together with the X-ray diffraction analysis of acetonide 3 and chemical correlation with (-)-(13E)-labd-13-ene-8α,15-diol (6), whose absolute configuration was also confirmed by X-ray analysis of its dibromo derivative 7. The epimeric labdenediols 8 and 9, the known labdanes 6 and 11, and the acylsucroses 12 and 13 were also isolated. Labdanes 6 and 11 showed moderate anti-inflammatory activities in the induced ear edema model.

Microwave-assisted synthesis and antimicrobial evaluation of novel spiroisoquinoline and spiropyrido[4,3-d]pyrimidine derivatives.

Bromination of N-substituted homophthalimides and tetrahydropyrido[4,3-d]-pyrimidine-5,7-diones produces 4,4-dibromohomophthalimide and 8,8-dibromo-tetrahydropyrido[4,3-d]pyrimidine-5,7-dione derivatives, respectively, that can be used as precursors for spiro derivatives. The dibromo derivatives react with different binucleophilic reagents to produce several spiroisoquinoline and spirotetrahydropyrido[4,3-d]-pyrimidine-5,7-dione derivatives, respectively. Reaction of the dibromo derivatives with malononitrile produces dicyanomethylene derivatives which react with different binucleophiles to produce new spiro derivatives. All new compounds are prepared by using the usual chemical conditions and microwave assisted conditions. The latter conditions improved the reaction yields, reduced reaction times and ameliorated the effects on the surrounding environment as the reactions are carried out in closed systems. Structures of the newly synthesized compounds are proved using spectroscopic methods such as IR, MS, 1H-NMR and 13C-NMR and elemental analyses. Some of the newly synthesized compounds were tested for their antimicrobial activities, whereby four of them showed moderate activities and the rest showed low or no activities towards the investigated species.

Vanadium(V) complexes of a tripodal ligand, their characterisation and biological implications.

The reaction of the tripodal tetradentate dibasic ligand 6,6'-(2-(pyridin-2-yl)ethylazanediyl)bis(methylene)bis(2,4-di-tert-butylphenol), H2L(1)I, with [V(IV)O(acac)2] in CH3CN gives the V(V)O-complex, [V(V)O(acac)(L(1))] 1. Crystallisation of 1 in CH3CN at ∼0 °C gives dark blue crystals of 1, while at room temperature it affords dark green crystals of [{V(V)O(L(1))}2μ-O] 3. Upon prolonged treatment of 1 in MeOH, [V(V)O(OMe)(MeOH)(L(1))] 2 is obtained. All three complexes were analysed by single-crystal X-ray diffraction, depicting a distorted octahedral geometry around vanadium. In the reaction of H2L(1) with V(IV)OSO4 partial hydrolysis of the tripodal ligand results in the elimination of the pyridyl fragment of L(1) and the formation of H[V(V)O2(L(2))] 4 containing the ONO tridentate ligand 6,6'-azanediylbis(methylene)bis(2,4-di-tert-butylphenol), H2L(2)II. Compound 4, which was not fully characterised, undergoes dimerization in acetone yielding the hydroxido-bridged [{V(V)O(L(2))}2μ-(OH)2] 5 having a distorted octahedral geometry around each vanadium. In contrast, from a solution of 4 in acetonitrile, the dinuclear compound [{V(V)O(L(2))}2μ-O] 6 is obtained, with a trigonal bipyramidal geometry around each vanadium. The methoxido complex 2 is successfully employed as a functional catechol-oxidase mimic in the oxidation of catechol to o-quinone under air. The process was confirmed to follow a Michaelis-Menten type kinetics with respect to catechol, the Vmax and KM values obtained being 7.66 × 10(-6) M min(-1) and 0.0557 M, respectively, and the turnover frequency is 0.0541 min(-1). A similar reaction with the bulkier 3,5-di-tert-butylcatechol proceeded at a much slower rate. Complex 2 was also used as a catalyst precursor for the oxidative bromination of thymol in aqueous medium. The selectivity shows quite interesting trends, namely when not using excess of the primary oxidizing agent, H2O2, the para mono-brominated product corresponds to ∼93% of the products and no dibromo derivative is formed.

Near-infrared luminescent Sn(IV) complexes of N-confused tetraphenylporphyrin: Effect of axial anion coordination

Novel tin(IV) halo complexes of an N-confused tetraphenylporphyrin with different axial ligands have been synthesized and characterized by various spectroscopic methods including X-ray crystallographic analysis. The molecular structures of the dichloro and dibromo derivatives possess perfect octahedral geometries, which are nearly comparable to the corresponding regular porphyrin complexes. In contrast, the iodide/triiodide complex obtained by a same reaction manner, demonstrated that the tin(IV) cation is slightly displaced towards axially coordinated iodide anion, giving rise to the different electronic structure due to the tautomeric form of N-confused porphyrin ligand. These structural differences reflected to the distinct photophysical and electrochemical properties. The Sn(IV) complexes are near IR luminescent, however the unsymmetrical axial coordination of iodide and triiodide anions in the tin(IV) N-confused porphyrin complex allows, in particular, the longer emission lifetimes and a smaller singlet-triplet energy gap, which were investigated by steady-state and time-resolved spectroscopies as well as theoretical calculations.

Determination of Acrylamide and Acrolein in Smoke from Tobacco and E-Cigarettes

Acrylamide and acrolein are two short-chained hazardous compounds with neurotoxic, carcinogenic, and mutagenic effects. The aim of this paper is to describe a fast and simple procedure for simultaneous determination of both acrylamide and acrolein under standard conditions, suggest a suitable calibration protocol for custom analysis, and demonstrate its applicability to the analysis of gaseous products from, e.g., cigarettes, cigars, or electronic cigarettes. A gas chromatography–mass spectrometry (GC–MS) method was developed to quantify acrylamide and acrolein in smoke vapor from electronic cigarettes, tobacco cigarettes, and cigars. Nonionic and highly polar molecules with a low boiling point and molecular mass need a suitable derivatization method to achieve appropriate retention and selectivity on commonly used relatively nonpolar stationary phases and to enhance the molecular mass for easy MS detection. The derivatization of acrylamide and acrolein was carried out by a bromination method with elemental bromine. The dibromo derivatives were extracted into an organic solvent and following a dehydrobromination procedure the samples were injected into the GC–MS system. Important experimental parameters were varied, after which the bromination time was defined as 30 min, and the injector temperature and the starting temperature of gradient were set at 280 and 50 °C respectively. Acrolein was found in all tested samples, while acrylamide was detected only in smoke from normal tobacco. Possible mechanisms for the formation of these unsaturated compounds in the samples are discussed. After its validation the newly developed method was successfully and reliably applied to the analysis of both compounds. This short method provides an easy way to determine acrylamide and acrolein in gaseous samples.

Synthesis and Antimicrobial Evaluations of 1,3,4‐Thiadiazoline‐based Bisheterocyclics

The bisthiadiazolines (4a, 4b, 4c, 4d, 4e, 4f, 4g) were synthesized from the cyclization of bisthiosemicarbazones (3a, 3b, 3c, 3d, 3e, 3f, 3g) by refluxing under Ac2O medium. The intermediates were obtained from the reactions of dibenzaldehydes (2a, 2b, 2c, 2d, 2e, 2f, 2g) with thiosemicarbazide by refluxing in the presence of dry EtOH/HCl. The latter were prepared in good yields from the O‐alkylation of 3‐hydroxybenzaldehyde with suitable dibromo derivatives under the alkaline conditions. The structures of prepared compounds were determined from rigorous analysis of their spectral parameters (UV–vis, IR, 1H NMR, 13C NMR and ESI‐MS). The newly prepared compounds were screened for their antimicrobial activity against seven bacterial and five fungi strains using serial tube dilution method.

Bromide-bromate Couple of Varying Ratios for Bromination, Vicinal Functionalisation and Oxidation in a Clean Manner

The review highlights applications of bromide-bromate couple in organic synthesis. The couple having 5:1 mole ratio of bromide to bromate is useful for preparation of dibromo derivatives from alkenes/alkynes. The 2:1 couple affects substitution with high bromine atom efficiency. Vicinal functionalization of olefins has also been studied. The 1:8 bromide-bromate couple has proved promising in several oxidation reactions, the performance exceeding that of bromate alone. This reagent was also the most effective for deiodination of styrene-based iodohydrins with concomitant rearrangement by a novel pathway. In all the cases the reagents were activated through in situ acidification. The 5:1 reagent is obtained as intermediate during liquid bromine manufacture and the other reagents were prepared from it using ClO-. Liquid bromine could be avoided in the product life cycle. Keywords: Bromide-bromate couples, direct preparation from bromine intermediate, In situ activation, reagents for green bromination and oxidation, regeneration and reuse.

ChemInform Abstract: Routes to Some 3,6‐Disubstituted Phthalonitriles and Examples of Phthalocyanines Derived Therefrom: An Overview

The paper reviews a selection of synthetic pathways that provide access to 3,6-disubstituted phthalonitriles, precursors for the synthesis of 1,4,8,11,15,18,22,25-octasubstituted phthalocyanine derivatives. Early routes using Diels–Alder reactions for the synthesis of 3,6-dialkyl, 3,6-dialkoxymethyl, 3,6-dialkenyl and 3,6-diphenylphthalonitriles are appraised. However, the emphasis of the review focuses on the scope and applications of 2,3-dicyanohydroquinone as a starting material for obtaining 3,6-disubstituted phthalonitriles. The earliest example of the use of 2,3-dicyanohydroquinone concerned its O-alkylation to afford 3,6-dialkoxyphthalonitriles. These are immediate precursors to near-infrared absorbing phthalocyanine derivatives. Triflation of 2,3-dicyanohydroquinone extends the scope of the compound for phthalocyanine synthesis; the bis-triflate derivative is susceptible to SNAr reactions and readily reacts with thiols to provide 3,6-bis(alkylsulfanyl) and 3,6-bis(arylsulfanyl)phthalonitriles. 3,6-Bis(phenylselenyl)phthalonitrile has also been obtained recently from the same precursor. Phthalocyanine derivatives obtained from them typically show a strongly bathochromically shifted Q-band absorption that is particularly sensitive to the central metal ion. The bis-triflate of 2,3-dicyanohydroquinone is also an ideal precursor for participation in cross-coupling reactions. Examples from the University of East Anglia group and elsewhere are presented which show the application of the nickel-catalyzed Negishi coupling reaction using alkylzinc halide derivatives. Yields of 3,6-dialkylphthalonitriles and 3,6-bis(substituted alkyl)phthalonitriles range from ca. 40 to 70%. Direct comparison for one example shows that the yield from the Negishi coupling method is higher than that using the Suzuki coupling protocol. Examples of the preparation of 3,6-diarylphthalonitriles from 2,3-dicyanohydroquinone bis-triflate using the Suzuki coupling reaction are reported with yields of the order of 65–70%. The review also includes a further application of 2,3-dicyanohydroquinone as a precursor to both monobromo and dibromo derivatives of 3,6-dibutoxyphthalonitrile. These compounds provide opportunities for cross-coupling at the brominated sites to provide more complex derivatives with the potential to serve as precursors of highly substituted phthalocyanine derivatives.

Routes to some 3,6-disubstituted phthalonitriles and examples of phthalocyanines derived therefrom: An overview

The paper reviews a selection of synthetic pathways that provide access to 3,6-disubstituted phthalonitriles, precursors for the synthesis of 1,4,8,11,15,18,22,25-octasubstituted phthalocyanine derivatives. Early routes using Diels–Alder reactions for the synthesis of 3,6-dialkyl, 3,6-dialkoxymethyl, 3,6-dialkenyl and 3,6-diphenylphthalonitriles are appraised. However, the emphasis of the review focuses on the scope and applications of 2,3-dicyanohydroquinone as a starting material for obtaining 3,6-disubstituted phthalonitriles. The earliest example of the use of 2,3-dicyanohydroquinone concerned its O -alkylation to afford 3,6-dialkoxyphthalonitriles. These are immediate precursors to near-infrared absorbing phthalocyanine derivatives. Triflation of 2,3-dicyanohydroquinone extends the scope of the compound for phthalocyanine synthesis; the bis-triflate derivative is susceptible to S N Ar reactions and readily reacts with thiols to provide 3,6-bis(alkylsulfanyl) and 3,6-bis(arylsulfanyl)phthalonitriles. 3,6-Bis(phenylselenyl)phthalonitrile has also been obtained recently from the same precursor. Phthalocyanine derivatives obtained from them typically show a strongly bathochromically shifted Q-band absorption that is particularly sensitive to the central metal ion. The bis-triflate of 2,3-dicyanohydroquinone is also an ideal precursor for participation in cross-coupling reactions. Examples from the University of East Anglia group and elsewhere are presented which show the application of the nickel-catalyzed Negishi coupling reaction using alkylzinc halide derivatives. Yields of 3,6-dialkylphthalonitriles and 3,6-bis(substituted alkyl)phthalonitriles range from ca. 40 to 70%. Direct comparison for one example shows that the yield from the Negishi coupling method is higher than that using the Suzuki coupling protocol. Examples of the preparation of 3,6-diarylphthalonitriles from 2,3-dicyanohydroquinone bis-triflate using the Suzuki coupling reaction are reported with yields of the order of 65–70%. The review also includes a further application of 2,3-dicyanohydroquinone as a precursor to both monobromo and dibromo derivatives of 3,6-dibutoxyphthalonitrile. These compounds provide opportunities for cross-coupling at the brominated sites to provide more complex derivatives with the potential to serve as precursors of highly substituted phthalocyanine derivatives.

Bromination-dehydrobromination/debromination of N-Methyl-N-(2-phenylethenyl)trifluoromethanesulfonamide

We have recently synthesized the first N-alkenylsubstituted trifluoromethanesulfonamide, N-methyl-N[(E)-2-phenylethenyl]trifluoromethanesulfonamide (I) [1]. With a view to obtain new trifluoromethanesulfonamide derivatives, we tried to synthesize adducts of I with various nucleophiles. However, compound I failed to react with methanol, ethanol, or diethylamine even on prolonged heating under reflux, but it readily took up bromine molecule in dioxane, and the resulting dibromo derivative readily underwent dehydrobromination by the action of alcoholic alkali (Scheme 1). 10.9 Hz), and a doublet at δ 6.58 ppm (J = 9.5 Hz) with a lower intensity. The intensity of the signal at 5.15 ppm was equal to the overall intensity of the signals at δ 6.51 and 6.58 ppm; the intensity ratio of the major and minor downfield signals was about 8 : 1. Assuming that the signal at δ 5.15 ppm is a superposition of two doublets corresponding to the downfield signals at δ 6.51 and 6.58 ppm, we can conclude that adduct II is a mixture of two diastereoisomers at a ratio of 8 : 1. These findings are consistent with the presence in the F NMR spectrum of II of two signals at δF –73.95 and –72.46 ppm with the same intensity ratio. Insofar as initial compound I is trans isomer [1], the major product should be stereoisomer IIa in agreement with the generally preferred trans-addition pattern. This is also supported by the results of HF/6-311G** calculations [2], according to which the energy of isomer IIa is lower by 1.3 kcal/mol than that of IIb. ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 6, pp. 924–926. © Pleiades Publishing, Ltd., 2013. Original Russian Text © I.V. Ushakova, B.A. Shainyan, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 6, pp. 938–939.