Six-membered heterocycles

Bogatskii, A. V.; Bogatskaya, Z. D.; Samitov, Yu. Yu.; Andreeva, A. A.

doi:10.1007/bf00486752

Cited by 2 publications

(3 citation statements)

References 4 publications

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“…The cis and trans isomers of 2,5-dialkyl-1,3-dioxanes have identical reactivity toward the acyclic boric esters; their ratio, determined earlier in [22], does not change in the range between 30:70 and 40:60 respectively [9,10]. However, the position changes in the case of 4,5-dialkyl-1,3-dioxanes, the stereochemistry of which was investigated in [23]; according to GLC, cis-4-methyl-5-isopropyl-1,3-dioxane reacts with the acyclic boric substrate more rapidly that the trans form (Table 3) [24].…”

Section: Borylation Of 13-dioxanesmentioning

confidence: 96%

Borylation of saturated heterocycles with several heteroatoms. (Review)

Кузнецов

2006

Chem Heterocycl Compd

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New examples of the borylation of a series of five-and six-membered saturated 1,3-and 1,3,2-heterocycles with the formation of cyclic boric esters are described. The probable mechanism of the reaction is discussed.A promising trend in the synthesis of cyclic boric esters, which are important reagents in organic chemistry, is the reaction of alicyclic boron substrates with saturated 1,3-or 1,3,2-heterocycles.XY 2 Z = O, NR; X = CR 1 R 2 , SiR 1 R 2 , S=O, GePh 2 , As(O)Ph; Y = OR, Cl; n = 0, 1 + Z Z + Early papers on this subject, which appeared in the second half of the twentieth century, were fragmentary in nature and were devoted to the borylation of 1,3-dithia-3-silacyclopentanes [1, 2], bis(1,3-diphenylimidazolidin-2-ylidene) [3], substituted 1,3-dioxanes [4][5][6][7], and six-membered silicon-and nitrogencontaining heterocycles [8]. In the last decade, however, it has been possible to discover interesting new examples of such reactions, to investigate their occurrence and stereochemistry in detail, and to obtain information about their probable mechanism.

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Section: Borylation Of 13-dioxanesmentioning

confidence: 96%

Borylation of saturated heterocycles with several heteroatoms. (Review)

Кузнецов

2006

Chem Heterocycl Compd

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“…The main attention was generally given to stereoisomeric acetals: the structure of individual cis and trans isomers, as well as parameters of configurational equilibrium were studied with a view to estimate the Gibbs conformational energy of substituents [2,[4][5][6]. On the other hand, cyclic formaldehyde acetals are characterized by greater conformational mobility and are very convenient models for studying the effect of heteroatoms on conformational parameters of cyclohexane heteroanalogs [7].…”

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confidence: 99%

“…EXPERIMENTAL 1,3-Dioxanes I-III [4][5][6]22] and IV [7] were reported previously. The 1 H NMR spectrum of a 10% solution of dioxane I in CDCl 3 was measured on a Bruker AM-300 spectrometer (300 MHz) using tetramethylsilane as external reference.…”

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confidence: 99%

Conformational analysis of 5-substituted 1,3-dioxanes

Kuramshina

Кузнецов

2010

Russ J Org Chem

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Quantum-chemical study on the potential energy surface of 5-alkyl-and 5-phenyl-1,3-dioxanes at the RHF/6-31G(d) level of theory revealed two pathways for conformational isomerizations of the equatorial and axial chair conformers. Potential barriers to this process were estimated. The Gibbs conformational energies ∆G° of substituents at C 5 in the 1,3-dioxane ring were determined on the basis of experimental ( 1 H NMR) and theoretical vicinal coupling constants, which turned out to be consistent with published data. I, R = Et; II, R = i-Pr; III, R = t-Bu; IV, R = Ph.Interest in structural studies on 1,3-dioxanes is determined by specificities of their structure and the use of these compounds as reagents in fine organic synthesis [1-3]. The main attention was generally given to stereoisomeric acetals: the structure of individual cis and trans isomers, as well as parameters of configurational equilibrium were studied with a view to estimate the Gibbs conformational energy of substituents [2, 4-6]. On the other hand, cyclic formaldehyde acetals are characterized by greater conformational mobility and are very convenient models for studying the effect of heteroatoms on conformational parameters of cyclohexane heteroanalogs [7]. Computer simulation in terms of nonempirical quantum-chemical calculations previously showed that the global minimum on the potential energy surface (PES) of unsubstituted 1,3-dioxane [8,9], as well as of 2-methyl-[10], 4-methyl-[11], 4-phenyl-[12], 5-methyl-[13], and 5-isopropyl-1,3-dioxanes [14], corresponds to chair (C) or equatorial chair conformer (C eq ). Local minima are occupied by axial chair (C ax ), 1,4-twist (1,4-T), and 2,5-twist conformers (2,5-T), while halfchair, sofa, and unsymmetrical boat conformers give rise to maxima on the potential energy surface. According to the data of microwave spectroscopy, the carbon fragment in 5-methyl-1,3-dioxane is more flattened than the heteroatom-containing fragment of the ring [15]. In the present work we studied probable paths for conformational isomerization of 5-alkyland 5-phenyl-1,3-dioxanes I-IV in terms of the RHF/6-31G(d) quantum-chemical approximation using HyperChem software [16]. According to the 1 H NMR data, conformational equilibrium of compounds I-IV at room temperature is displaced toward C eq conformer (Scheme 1) [2]. Scheme 1.We have revealed general pattern of conformational transformations and localized intermediate minima and maxima on the PESs of dioxanes I-IV. The results of calculations suggest two paths for the conformational isomerization C eq ↔ C ax , which are analogous to those found previously for unsubstituted 1,3-dioxane, as well as for 2-methyl-, 5-methyl-, and 5-isopropyl-1,3-dioxanes [9,10,13,14]. In all cases, the global minimum corresponds to equatorial chair conformer (C eq ), while conformer 1,4-T has the highest energy (Table 1). Increase in the conformational volume of the R substituent (I < II < III) is accompanied by increase in the energy difference (∆E) between conformers C eq and C ax , as well as...

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Six-membered heterocycles

Cited by 2 publications

References 4 publications

Borylation of saturated heterocycles with several heteroatoms. (Review)

Borylation of saturated heterocycles with several heteroatoms. (Review)

Conformational analysis of 5-substituted 1,3-dioxanes

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