Organoboron Compounds : XI. Mass spectral studies on some 2-phenyl-1,3,2-dioxaborinanes

2-Phenyl-1,3,2-dioxaborinanes have been found to undergo electron impact-induced rearrangements resulting in the formation of hydrocarbon ions.     

Stereochemistry of 2,3-disubstituted 1,3,2-dioxaborinanes

According to¹H NMR spectroscopic data, molecules of 2,4-disubstituted 1,3,2-dioxaborinanes exist in the preferred sofa conformation with equatorial alkyl groups at C₍₄₎. This conclusion has been confirmed by calculation of the optimal geometry of the ring of the cyclic boron esters by the MM2 molecular mechanics method. A. V. Bogatskii Physicochemical Institute, Ukraine National Academy of Sciences, Odessa 270080. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1574–1578, November, 1997.     

Mass spectra of a series of 2-p-substituted phenyl-1,3,2-dioxaborolanes

The mass spectra of a series of 2-p-substituted phenyl-1,3,2-dioxaborolanes have been examined and compared with the mass spectrum of 2-phenyl-1,3,2-dioxaborolane. Formation of the substituted ion [C₇H₆X]⁺ by electron impact induced rearrangement has been found to be influenced significantly by the presence and nature of the substituent at the para position of the phenyl ring.     

Conformational analysis of 2,4-dialkyl-1,3,2-dioxaborinanes

Computer modeling using the quantum-chemical empirical MM+ method and nonempirical RHF//6-31G(d), MP2//6-31G(d), and, in individual cases, RHF//3-21G methods was employed to study the potential energy surface of 2,4-dialkyl-1,3,2-dioxaborinanes. The optimal geometry and ¹H NMR spectral data gave values for ∆G ⁰ of the methyl and hexyl substituents at C-4 of the heterocyclic ring equal to 0.6 and 1.6 kcal/mol, respectively.     

Conformational analysis of 2-methyl-5-alkyl- and 5-aryl-1,3,2-dioxaborinanes

Quantum chemical study of conformational isomerization of 2-methyl-5-alkyl- and 5-aryl-1,3,2-dioxaborinanes using RHF/6-31G(d) method led to the conclusion that the equilibrium between equatorial and axial sofa conformers is shifted to the latter form. Based on the experimental and theoretically calculated vicinal coupling constants J _HH the quantitative conformational composition and the values of ΔG ⁰ for substituents at the C⁵ ring atom were established.     

Configuration and isomerization of 2,4,5-substituted 1,3,2-dioxaborinanes

Reaction of esters of isobutylboronic acid with 2-methyl-1-phenyl-1,3 propanediol and 2-benzyl-1,3-butanediol gave 2-isobutyl-5-methyl-4-phenyl- and 4-methyl-5-benzyl-1, 3, 2-dioxaborinanes respectively, with a preponderance of the cis-isomers in the mixtures. Cis-2-isobutyl-5-methyl-4-phenyl-1, 3, 2-dioxaborinane was converted to thetrans isomer on heating to 150°C with a catalytic amount of ZnCl₂.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1291–1294, September, 1995.     

Stereochemistry of the formation of 2-alkyl-4,5-dimethyl-1,3,2-dioxaborinanes

It is demonstrated with the help of¹H and¹³C NMR spectroscopy and GLC that the formation of the stereoisomers of 2-alkyl-4,5-dimethyl-1,3,2-dioxaborinanes from 2-methyl-1,3-butanediol and acyclic boric acid esters occurs stereospecifically. This conclusion was confirmed by calculations of the optimal geometries and relative energies of the molecules of thecis-andtrans-isomers of model 4,5-dimethyl-1,3,2-dioxaborinanes and the proposed intermediate with a tetravalent boron atom using the method of molecular mechanics.A. V. Bogatskii Physicochemical Institute, National Academy of Sciences of Ukraine, Odessa 270080, Ukraine. Institute of Organic Chemistry, Ufa Science Center, Russian Academy of Science, Ufa 450054, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 400–404, March, 1998.     

Conformation of 2,5-substituted 1,3,2-dioxaborinanes studied by NMR

The conformation of a series of 2,5-substituted 1,3,2-dioxaborinanes is studied by PMR. The preferred conformation for the majority of compounds has an equatorial group on atom C₍₅₎. The 5-nitroderivative exists in the conformation with an axial nitro group.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1107–1109, August, 1990.     

Synthesis and some properties of planar 4-diphenylphosphino-1,3,2-dioxaborinanes

Fused 1,3,2-dioxaborinanes, derivatives of 4-diphenylphosphino- and 4-diphenylphosphoryl-4H-1, 3-dioxa-2-boraphenanthrenes, and their complexes with amines have been synthesized. According to X-ray diffraction data, the complex of 2-phenyl-4-diphenylphosphoryl-4H-1, 3-dioxa-2-boraphenanthrene with butylamine exists as a dimer due to the formation of intermolecular hydrogen bonds.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1649–1655, September, 1994.The present work was financially supported by the International Science Foundation (grant No. RHBOOO).     

Computer modelling of the conformational equilibrium of 2-and 2,5,5-substituted 1,3,2-dioxaborinanes

Empirical, semiempirical, and nonempirical quantum-chemical methods were used to study the conformational equilibrium of 2,5,5-substituted 1,3,2-dioxaborinanes. The sofa invertomers were found to correspond to the local and global minima on the potential energy surface. The position of the equilibrium between these forms is a function of the substituents at C₍₅₎ of the heterocycle. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 12, pp. 1860–1865, December, 2007.     

Conformational Composition of Stereoisomers of 2-Alkyl-5-isopropyl-4-methyl-1,3,2-dioxaborinanes

¹H and ¹³C NMR spectroscopy was used to assign the configuration of a mixture of stereoisomers of 2-alkyl-5-isopropyl-4-methyl-1,3,2-dioxaborinanes with different ratios of the cis and trans forms. These forms differ in the configuration of C⁽⁴⁾ in the ring. The results of MM+ and AM1 calculations for the optimal geometry indicate high conformational flexibility of both isomers, which exist in an equilibrium mixture of sofa and half-chair conformers.     

Chemical ionization induced competing and consecutive heterolytic ring cleavages in the mass spectra of substituted tetrahydro-1,3,2-oxazaphosphorin-2-oxides

The chemical ionization mass spectra of some substituted heterocyclic systems, viz. tetrahydro-1,3,2-oxazaphosphorin-2-oxides, reveal polar cycloreversion reactions. The zwitterion intermediate formed by the heterolysis of the C? O bond undergoes stepwise clean heterolysis further resulting in the expulsion of the potential nucleophilic and electrophilic groups. The competitive and consecutive heterolysis of the ring bonds leads to the formation of the protonated phenylimine ions. Competing with heterolysis, elimination reactions involving hydrogen transfer leading to the formation of α-phenylethyl ions are also observed. The chemical ionization mass spectrometry of the heterocyclic system shows many features of the Grob type of fragmentation mechanism.     

Analysis of the conformational composition of 5-nitro-1,3,2-dioxaborinanes

Empirical MM2 and semiempirical AM1, MNDO, and MINDO/3 calculations were carried out to determine the energy with complete geometrical optimization of 5-nitro-1,3,2-dioxaborinanes as well as of model 5-nitro-1,3-dioxanes, 4-nitroborinane, and nitrocyclohexane. Comparison of the experimental and calculated coupling constants and the energy data indicates that the sofa conformation with an axial nitro group perpendicular to the plane of molecular symmetry predominates for cyclic borate esters.A. V. Bogatskii Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 270080 Odessa, Ukraine. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1065–1072, August, 1999.     

PMR study of the conformational behavior of 2,5,5-trisubstituted 1,3,2-dioxaborinanes

The conformational behavior of 2,5,5-trisubstituted 1,3,2-dioxaborinanes was studied by PMR spectroscopy. Molecules with similar substituants at C(₅) are in a state of rapid ring inversion between two energetically equivalent forms. In the case of different substituents, the inversion proceeds between energetically inequivalent states with a shift in the equilibrium toward one of them.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 558–561, April, 1986.     

Structure and reactions of benzo-4-diphenylphosphino-2-phenyl-1,3,2-dioxaborinane

The crystal structure of 5,6-benzo-4-diphenylphosphino-2-phenyl-1,3,2-dioxaborinane 1 indicates the occurrence of an interaction between the π-systems of the 1,3,2-dioxaborinane ring and the appropriate phenyl group of the diphenylphosphino group. Complexes of compound 1 with PtCl₂, PdCl₂, and Cul were synthesized. Compound 1 and its complexes are readily hydrolyzed in solution to give diphenylphosphine and its corresponding complexes (NMR).     

Molecular and crystal structure of 2-phenyl-2-oxo-5,6 -benzo-1,3,2-dioxaphosphepine

The seven-membered heterocycle in the crystal structure of 2-phenyl-2-oxo-5,6-benzo-1,3,2-dioxaphosphepine has distorted (asymmetric) twist conformation and the plane of the phenyl substituent at the phosphorus atom does not coincide with the bisector of the plane of the OPO fragment of the heterocycle and is not perpendicular to it.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 214–217, January, 1991.     

Electron impact induced fragmentations of 2-chlorovinyl methyl sulphides

A series of 2-chlorovinyl methyl sulphides, CH₃SCR¹?CR²Cl (R¹, R² = H, Me, Et, t-Bu, Ph; R¹ = H, R² = CH₃) has been analysed under electron impact conditions. The most significant common fragmentations involve primary loss of Cl˙ and methyl radicals. Analysis of the phenyl-substituted derivative suggests that loss of CH₃˙ is a lower activation energy process than loss of Cl˙. The characteristic loss of CH₃SCl from the same derivative has been examined with respect to the structure of the resulting fragment by means of suitable model compounds.