Synthesis and nonchair conformations of 2,2-disubstituted 4,4-dimethyl-1, 3-dioxanes

The fundamental possibility of the synthesis of 2-substituted 1,3-dioxanes by reaction of 1,3-dioxanium perchlorates with organometallic compounds is demonstrated. A method for the synthesis of acyl derivatives of heterocycles was developed on the basis of these compounds. The existence of 2,2,4,4-substituted 1,3-dioxanes in the twist conformation was shown by ¹H NMR spectroscopy; the twist conformation is explained by the effect of nonbonded 1,3-syn-axial interactions.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1172–1179, September, 1978.     

Synthesis,structure, and stereochemistry of 2-alkyl-4,4,5-trimethyl- and 2-alkyl-4,4,6,6-tetramethyl-1,3-dioxanium perchlorates

A number of 2-alkyl-4,4,5-trimethyl- and 2-alkyl-4,4,6,6-tetramethyl-1,3-dioxanium perchlorates were obtained by acylation of 1,3-diols in the presence of 70% perchloric acid. Acid-catalytic cleavage of the heteroring with subsequent cyclization to 2-alkyl-1,3-dioxanium perchlorates occur in the reaction of 2-aryl(alkyl)-substituted and 2-unsubstituted 1,3-dioxanes with carboxylic acid anhydrides and 70% HClO₄. Hypothetical detachment of a hydride ion by means of the acceptor acylium cation does not occur under the investigated conditions. The structures of the synthesized perchlorates were studied by PMR spectroscopy and it was shown that 1,3-dioxanium cations at room temperature exist in a state of rapid conformational isomerization of the chair-chair form. The rate of interconversion of the 2,4,4-trimethyl-1,3-dioxanium cation decreases appreciably as the temperature is reduced to –90°. as evidenced by marked broadening of the lines of the protons of the gemdimethyl groupings.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 182–186, February, 1977.     

Synthesis and conformation of 2-silylethynyl-substituted 2,4,4,6-tetramethyl-1,3-dioxanes

Reaction of 2,4,4,6-tetramethyl-1,3-dioxanium perchlorate with lotsich reagents led to the synthesis of new silylethynyl-substituted 2,4,4,6-tetramethyl-1,3-dioxanes. According to the data of¹H and¹³C NMR and x-ray diffraction analysis, it was established that the 1,3-dioxane ring of the products obtained has the chair conformation.Kuban' State Technological University, Krasnodar 350072, Russia. Ufa State Oil Technical University, Ufa 450062, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 4, pp. 487–493, April, 1998.     

Steerochemistry of heterocycles.

The stereochemical peculiarities of substituted 1,3-dioxanes and 1,3-dithianes are discussed. The high probability of the existence of flexible conformations in these series, the considerable energy preference of the 5-C-axial position in the chair conformation of 1,3-dioxanes and 1,3-dithianes, and the definite preference of the 2-C-axial position in the chair conformation of 1,3-dithianes as compared with the axial conformations of the cyclohexane type are noted. The PMR spectra of stereoisomeric 2,5-dimethyl-5-isopropyl-1,3-dioxanes, 2-methy-l5-isopropyl-1,3-dithianes, and 2,2,5-trimethyl-1,3-dithiane are described, and their configurations and preferred conformations are proved. The results of a study of the epimerization of stereoisomers of substituted 1,3-dioxanes and 1,3-dithianes are examined, and the conformational energies of individual substituents in the 5-position of these cyclic systems are calculated on the basis of this examination.See [48] for communication IV.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 582–592, May, 1971.     

Synthesis of 2-R-1,3-dioxanes, derivatives of functionally substituted aldehydes of vanillin series

By the condensation of substituted aldehydes of vanillin series with 1,3-propanediol in boiling benzene in the presence of sulfo cation exchanger FIBAN K-1 as catalyst functionally 2-R-substituted 1,3-dioxanes were synthesized.     

Comparative conformational analysis of 2,2-dimethyl and 2,2,5-trimethyl-1,3-dioxanes and their 2-heteroanalogs with silicon and germanium atoms

Comparative conformational analysis of 2,2-dimethyl- and 2,2,5-trimethyl-1,3-dioxanes as well as their 2-heteroanalogs with silicon and germanium atoms has been performed by means of computer simulation using HF/pVDZ, hybrid DFT PBE/3ξ, and RI-MP2/λ2 methods. The potential energy surface for all the studied compounds has revealed the presence of the chair and 2,5-twist conformers. The latter form, in the case of substituted 1,3-dioxa-2-silacyclohexanes at the HF/pVDZ level, is a transition state rather than an intermediate minimum. The molecules of 2-sila- and 2-germa-1,3-dioxacyclohexanes exhibit an enhanced conformational flexibility as compared to the 1,3-dioxanes.     

Synthesis and properties of 1,3-dioxanium salts (review)

Syntheses, structures, spectral characteristics, and chemical properties of 1,3-dioxanium salts are reviewed.Kuban State Technological University, Krasnodar 350072, Russia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 291–316, March, 1999.     

Studies in organic mass spectrometry. XVIII—The effect of branching in the sidechain upon the fragmentation of 4,6-dialkyl-1,3-dioxanes

The presence of a 2′-tertiary hydrogen atom has a profound influence on the general fragmentation pattern of 4,6-dialkyl-1,3-dioxanes. Branching at the 2′-position induces a double hydrogen transfer reaction which is absent in the spectra of 4,6-n-alkyl-1,3-dioxanes.     

An unexpected 1,2-hydride shift in phosphoric acid-promoted cyclodimerization of styrene oxides under solvent-free conditions. A synthetic route towards 2,4-disubstituted 1,3-dioxolanes

A 1,2-hydride shift in the phosphoric acid-promoted cyclodimerization of styrene oxide and its chloro derivatives under solvent-free conditions leading to 2,4-disubstituted 1,3-dioxolanes is described. Methoxy substituents on the aromatic ring of the styrene oxide prevent the 1,2-hydride shift reaction leading to substituted 1,4-dioxanes. A possible mechanism for the formation of the 1,3-dioxolanes is proposed.     

Conformational analysis of six-membered cyclic carbonates

The conformational isomerization of 2-oxo-1,3-dioxane and its methyl analogs was investigated by means of ab initio RHF//6-31G(d,p) and MP2//6-31G(d,p) quantum-chemical methods. It is shown that in comparison with 1,3-dioxanes the potential energy surface of the mentioned compounds has a fewer number of stationary points and includes two minima corresponding to conformers of sofa or distorted sofa configuration and one maximum corresponding to 2,5-twist form. The value of potential barrier of interconversion of cyclic carbonates is significantly lower than that of the analogously substituted 1,3-dioxanes.     

1,4-Dioxanes as products of the oxidation of N-vinyllactams

2, 5-Disubstituted 1,4-dioxanes have been obtained by the oxidation of N-vinyllactams, represented by N-vinylpyrrolidone, N-vinylpiperidone, and N-vinylcaprolactam, and their structure has been shown by independent synthesis: the reaction of trans-2, 5-dichloro-1,4-dioxanes with alkali-metal salts of the lactams also gave 2,5-di(N-2-oxopolymethyleneimino)-1,4-dioxanes.     

1,4-Dioxanes as products of the oxidation of N-vinyllactams

2, 5-Disubstituted 1,4-dioxanes have been obtained by the oxidation of N-vinyllactams, represented by N-vinylpyrrolidone, N-vinylpiperidone, and N-vinylcaprolactam, and their structure has been shown by independent synthesis: the reaction of trans-2, 5-dichloro-1,4-dioxanes with alkali-metal salts of the lactams also gave 2,5-di(N-2-oxopolymethyleneimino)-1,4-dioxanes.     

Reaction of substituted 1,3-dioxanes with the disobutyl ester of isobutylboric acid

The reaction of subsitituted 1,3-dioxanes with the diisobutyl ester of isobutylboric acid leads to the corresponding 1,3,2-dixaborinanes. The determining factor in the reactivity of the 1,3-dioxanes is the degree of substitution of the acetal atom.A. V. Bogatskii Physicochemical Institute, National Academy of Sciences of the Ukraine, Odessa 270080. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 160–162, February, 27, 1995. Original article submitted February 27, 1995.     

Preparation of 1,3-dioxanium perchlorates

2,4,4,6,6-Substituted 1,3-dioxanium perchlorates were obtained by acylation of ditertiary 1,3-diols with carboxylic acid anhydrides in the presence of 70% perchloric acid.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 169–172, February, 1976.     

Synthesis of Alkyl 4-Ethyn(en)yl-6-methyl-1,3-dioxane-5-carboxylates

Russian Journal of Organic Chemistry - Condensations of chloromethyl propargyl(allyl) ethers with alkyl 3-oxobutanoates in the presence of pyridine gave substituted 1,3-dioxanes.     

Chemoselective conversion of aromatic epoxide and 1,2-diol to 1,3-dioxane derivatives with phenyltrimethylammonium tribromide in the presence of a catalytic amount of antimony(III) bromide

trans-Stilbene oxide was oxidatively converted to 2-phenyl-1,3-dioxanes with phenyltrimethylammonium tribromide in the presence of various 1,3-diols and a catalytic amount of SbBr₃ in DMSO at room temperature. Aromatic 1,2-diol, such as hydrobenzoin, was similarly converted to 2-aryl-1,3-dioxane derivatives under the same reaction conditions.     

Ringdeformationen und rotameres Verhalten des Phenylrestes in 2,2-disubstituierten 1,3-Dioxanen

Introduction of substituents in position 2 of 1,3-dioxanes decreases the torsional angles of the OCH₂CH₂CH₂O moiety (_{4, 5}, _{5, 6}) indicating an enhanced flattening in this part of the molecule. In geminally substituted 2-alkyl-2-phenyl-1,3-dioxanes the phenyl group isaxial, andgonal with respect to the rotameric state, while in ortho substituted derivatives, e.g. 2-methyl-2-(o-methylphenyl)-1,3-dioxane theaxial phenyl ligand assumes an intermediate rotameric position. Theaxial preference is not influenced by intramolecular dipole—dipole interaction generated by a p-substituent in the phenyl group as is shown for various 2-methyl-2-(p-substitutedphenyl)-1,3-dioxanes.

---

---

Mit 5 Abbildungen

---

Herrn Prof. Dr.K. Kratzl zum 60. Geburtstag gewidmet.

---

Auszugsweise vorgetragen bei der Tagung des Vereins Österreichischer Chemiker in Wien am 20. März 1975.     

Reaction of 1,3-Dioxanes with Acetone Cyanohydrin

The reaction of 4-phenyl- and 4,4-dimethyl-1,3-dioxanes with acetone cyanohydrin leads to hydrolytically unstable 2-(1-hydroxy-1-methylethyl)-5,6-dihydro-1,3-oxazines, which are readily saponified in alkaline medium to the corresponding 1,3-amino alcohols.     

Arylolefins in modified prins reaction

Conclusions Acid-catalyzed cocondensation of formaldehyde and alkanals RCHO with styrene leads to 2-R-4-phenyl-1,3-dioxanes with equatorial orientation of substituent R in the 2-position, and with -methylstyrene to a mixture of 4-methyl-2-R-4-phenyl-1,3-dioxanes with axial and equatorial orientation of substituent R.The yield of the cocondensation products in this reaction reaches 60%.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 899–902, April, 1982.     

Synthesis and three-dimensional structure of 5,5-disubstituted 2-alkoxy-1,3-dioxanes

It was established by PMR spectroscopy that a chair conformation with an axial orientation of the alkoxy substituent is the primary conformation for 5,5-disubstituted (and unsubstituted) 2-alkoxy-1,3-dioxanes. As compared with alkyl-1,3-dioxanes, 2-alkoxy-1,3-dioxanes are characterized by reversal of the chemical shifts of the axial and equatorial protons attached to C₄, and C₆.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 9, pp. 1182–1185, September, 1981.