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.     

Synthesis of 2-phenylethynyl-1,3-dioxanes and their hydrolysis

2-Phenylethynyl substituted 1,3-dioxanes were obtained by the reaction of 1,3-dioxanium salts with an lotsich reagent. It was shown that they are readily hydrolyzed with the formation of a-acerylenic ketones. A simple new method is proposed for the synthesis of the latter without isolating the intermediate 1,3-dioxanes using the reaction of 4 substituted 2-methyl(phenyl, furyl)-1,3-dioxanium salts with hydroxymethyl- and phenylethynylmagnesium bromide as examples.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 193–197, February, 1996.     

O-17 NMR spectra of ring compounds. Correlation of 17O and 13C methyl substitution parameters

The ¹⁷O NMR spectra of 22 1,3-dioxanes, four exanes, four 4-heterooxanes, four tetrahydrofurans and four 1,3-dioxolanes have been recorded and methyl substitution parameters determined for the 1,3-dioxanes. The parameters, including γ_a, correlate linearly with corresponding ₁₃C parameters for methyloxanes.     

Research on furan acetal compounds

Furan 1,3-dioxanes were obtained by condensation of 2,2-dimethyl-1,3-propanediol with aldehydes of the furan series. The lithium derivatives of bromine-substituted 1,3-dioxanes were used for the synthesis of a number of alcohols.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 595–596, May, 1973.See [1] for communication V.     

Rh2(OAc)4-catalyzed reaction of 1,3-dioxanes with methyl diazoacetate

The reactions of methyl diazoacetate with 1,3-dioxanes in the presence of Rh₂(OAc)₄ afford 1,4-dioxepanes in up to 46% yields. The insertion of methoxycarbonylcarbene into the C—O bond occurs only in the case of 2-phenyl-1,3-dioxanes.     

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.     

Stereochemie der heterocyclen—XXXI : Die konfiguration und bevorzugte konformation substituierter 4-methyl-1,3-dioxane

The configuration and conformation of some stereoisomers of 4,5-, 4,5,5- and 2,2,4,5-substituted 1,3-dioxanes are examined. The stereospecifity of the reduction of alkylacetoacetic esters to 2-alkylbutandiols-1,3 and to 4,5-, 2,2,4,5-substituted 1,3-dioxanes is studied. ¹H-NMR-Data of cis- and trans-configurated 4,5- and 2,2,4,5-substituted 1,3-dioxanes are reported.     

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 mesomorphic properties of four-ring liquid crystals containing 2,3-difluorophenyl and 1,3-dioxane units

Two series of novel liquid crystalline materials were synthesized: 2-(2,3-difluoro-4-alkoxyphenyl)-5-[4-(4-alkylcyclohexyl)phenyl]-1,3-dioxanes (A _m-n and 2-(2,3-difluoro-4-alkylphenyl)-5-[4-(4-alkylcyclohexyl)phenyl]-1,3-dioxanes (B _m-n ). Their mesmorphic properties were characterized by polarizing optical microscopy and differential scanning calorimetry. All these compounds exhibit broad mesomorphic phases, and most of them show wide smectic C phases and the phase sequence Cr-SmC-SmA-N-I. The relationship between properties and chemical structures is discussed in detail.     

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.     

Research on furan acetal compounds

The configuration and preferred conformations of a number of stereoisomeric 2-(α-furyl) 1,3-dioxanes were established by PMR spectroscopy. It is shown that cis orientation of the NO₂ groups with respect to the furyl ring is primarily realized for 2-(α'-nitro-α-furyl)-5-ethyl-5-nitro-1,3-dioxanes.     

Synthesis and mesomorphic properties of four-ring liquid crystals containing 2,3-difluorophenyl and 1,3-dioxane units

Two series of novel liquid crystalline materials were synthesized: 2-(2,3-difluoro-4-alkoxyphenyl)-5-[4-(4-alkylcyclohexyl)phenyl]-1,3-dioxanes (A_m-n) and 2-(2,3-difluoro-4-alkylphenyl)-5-[4-(4-alkylcyclohexyl)phenyl]-1,3-dioxanes (B_m-n). Their mesmorphic properties were characterized by polarizing optical microscopy and differential scanning calorimetry. All these compounds exhibit broad mesomorphic phases, and most of them show wide smectic C phases and the phase sequence Cr-SmC-SmA-N-I. The relationship between properties and chemical structures is discussed in detail.     

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.     

On the preparation of 2-halo alkyl substituted 1,3-dioxolanes and 1,3-dioxanes

Several methods for the preparation of 2-perfluoromethyl-substituted 1,3-dioxolanes and 1,3-dioxanes were tried. The method of Nerdel for the preparation of 1,3-dioxolanes, making use of the condensation between carbonyl compounds and oxiranes, was found to be suitable for perhalogenated ketones and aldehydes, and may even be extended to oxetanes, affording 2-perhaloalkylated 1,3-dioxanes.The yield of the cyclic acetals drops with inreasing substitution.     

Research on furan acetal compounds

The possibility of the reduction of the furan ring to a tetrahydrofuran ring under the conditions of liquid-phase hydrogenation of 2-furyl-1,3-dioxanes on Raney nickel at atmospheric pressure is demonstrated. 2-Furyl or tetrahydro-2-furyl amino derivatives of 1,3-dioxane are formed in the case of 5-nitro-2-furyl-1,3-dioxanes as a function of the structure of the starting acetals. Data from the UV and IR spectra are presented.See [1] for communication IX.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 8, pp. 1026–1029, August, 1977.     

Synthesis,structure, and transformations of cyclic glycerol formals

Glycerol reacts with paraformaldehyde to give a mixture of 4-hydroxymethyl-1,3-dioxolane and 5-hydroxy-1,3-dioxane. Some transformations (alkylation and replacement of the OH groups with the Cl atoms) of the synthesized compounds were performed. The differences in NMR and mass spectra of the corresponding 1,3-dioxolanes and 1,3-dioxanes were revealed and discussed.     

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.     

Steric and electrostatic interactions in hexacyclic ring systems: The origin of the buttressing effect

Ring deformation in a number of 2-trichloromethyl-1,3-dioxanes could be traced in their ¹H NMR spectra from anomalies in coupling constants. No distortion occurs when the 2-substituent is a dichloromethyl or a tertiobutyl group, or when a 4-axial substituent is lacking. It was impossible to deduce the ring geometry from the vicinal coupling constants, but the nature of the ring deformation has been ascertained by NMR data (³J_exo, Δδ) and dipole moment calculations. Flexible conformations are not the origin of the observed anomalies. The rotomeric populations in 2-dichloromethyl-1,3-dioxanes has been evaluated and the origin of the buttressing effect, as caused by different substitution, has been disclosed.     

Alkoxy compounds

Twenty-six previously unreported 5-alkoxymethyl-2,5-dialkyl-1,3-dioxanes have been synthesized by the condensation of 2-alkoxymethyl-2-alkylpropane-1,3-diols with aldehydes. It has been shown by an analysis of the PMR spectra of these dioxanes that the 1,3-dioxanes considered are mixtures of two stereoisomers. In some cases these mixtures have been resolved into the individual isomers by vacuum fractionation in efficient columns. The configurations and conformations of the stereoisomeric 5-alkoxymethyl-2,5-dialkyl-1,3-dioxanes have been established by the NMR method; it has been shown that the lower-boiling isomers have the trans configuration and predominantly the chair conformation and the higherboiling isomers the cis configuration and predominantly an unsymmetrical boat conformation.For part XX, see [7].     

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.