ChemInform Abstract: RADICAL‐CHAIN TRANSFORMATIONS OF ACETALS IN A SOLUTION

Section: 3-dioxanesmentioning

confidence: 99%

Computer simulation of conformational transformations of 1,3-dioxanes and their 2-sila and 2-bora analogs

Кузнецов

2014

“…In particular, 4,4-dimethyl-1,3-dioxane is a starting compound in the large-scale manufacture of isoprene [1], as well as in laboratory syntheses of 3-amino alcohols [3]. Nonempirical computer simulations previously showed that the global minimum on the potential energy surface (PES) of unsubstituted [4] and 2-methyl- [5], 4-methyl- [6], 4-phenyl- [7], 4-trifluoromethyl- [8], 5-methyl- [9] and 5-isopropyl-substituted 1,3-dioxanes [10] is occupied by chair (C) or equatorial chair conformer.…”

mentioning

confidence: 99%

“…1,3-Dioxanes are classical model structures for conformational analysis; they possess interesting structural and a number of practically important properties and are used as reagents in large-scale and fine organic synthesis [1][2][3]. In particular, 4,4-dimethyl-1,3-dioxane is a starting compound in the large-scale manufacture of isoprene [1], as well as in laboratory syntheses of 3-amino alcohols [3].…”

mentioning

confidence: 99%

Conformational analysis of 4,4-dimethyl-1,3-dioxane

Faizullin

Mamleev

2011

The potential energy surface of 4,4-dimethyl-1,3-dioxane molecule was analyzed in terms of the density functional theory at the PBE/cc-pVDZ and B3PW91/aug-cc-pVDZ levels. Eight energy minima were revealed with account taken of enantiomeric structures, the corresponding transition states were found, and the most probable chair-chair conformational isomerization pathways were proposed. 1,3-Dioxanes are classical model structures for conformational analysis; they possess interesting structural and a number of practically important properties and are used as reagents in large-scale and fine organic synthesis [1-3]. In particular, 4,4-dimethyl-1,3-dioxane is a starting compound in the large-scale manufacture of isoprene [1], as well as in laboratory syntheses of 3-amino alcohols [3]. Nonempirical computer simulations previously showed that the global minimum on the potential energy surface (PES) of unsubstituted [4] and 2-methyl-[5], 4-methyl-[6], 4-phenyl-[7], 4-trifluoromethyl-[8], 5-methyl-[9]and 5-isopropyl-substituted 1,3-dioxanes [10] is occupied by chair (C) or equatorial chair conformer. Local minima correspond to axial chair, 1,4-twist (1,4-T), and 2,5-twist (2,5-T) conformers, and transition states (TS) have half-chair (HC), sofa (S), and unsymmetrical boat (B) structures. According to the microwave spectroscopy data, the carbon fragment in 5-methyl-1,3-dioxane is flatter than the heteroatom-containing moiety [11]. Unsymmetrically substituted cyclic formaldehyde acetals were found to be characterized by more complex PES [6][7][8]. However, contrary to the expectations, RHF/6-31G(d,p) study on conformational isomerization of unsymmetrically substituted 4,4-dimethyl-1,3-dioxane (I) revealed relatively small number of minima and maxima on the PES [12]. The goal of the present study was to analyze possible conformational isomerization pathways of 4,4-dimethyl-1,3-dioxane (I) with the use of PBE and B3PW91 hybrid exchangecorrelation functionals and cc-pVDZ Dunning's basis set built in Gaussian 98 [13].According to the 1 H NMR data [2], molecules I at room temperature undergo fast interconversion between two energy-degenerate chair conformers C 1 and C 2 with a fairly low energy barrier (Scheme 1).

“…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][2][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][5][6].…”

mentioning

confidence: 99%

Conformational analysis of 5-substituted 1,3-dioxanes

Kuramshina

Кузнецов

2010

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...