Ethyl Dithioacetate Research Articles

Low-temperature NMR studies of phenyl dithioacetate and ethyl dithioacetate

The 300.52 MHz proton NMR spectrum of phenyl dithioacetate in CD 2Cl 2 at −91°C shows separate methyl signals for the E and Z conformations, with populations of 0.09 and 0.91, respectively. The free-energy barriers at coalescence (−65°C) are 9.8 1 and 10.6 4 kcal/mol for the E → Z and Z → E conversions, respectively. Slow-exchange C 13 NMR spectra were also obtained for solutions in several solvents. The populations in 3:1 acetaldehyde acetone-d 6 were 0.12 and 0.88 at −92°C, as obtained from integration of the methyl carbon signals, and free-energy barriers at coalescence (−68°C) were 9.4 8 and 10.2 0 kcal/mol. Decoalescence was not observed at low temperatures for ethyl dithioacetate, probably due to a low population of the E isomer. The finding of an observable population of the E isomer for phenyl dithioacetate, but not for ethyl dithioacetate, is suggested to be related to the difference in hybridization and electronegativity of the two groups, with higher electronegativity favoring the E conformation.

Rotational isomerism in CH3C(S)SCH3 and CH3C(S)SCH2CH3: a combined vibrational spectroscopic and ab initio study

Rotational isomerism in CH3C(S)SCH3 and CH3C(S)SCH2CH3 is examined by combining a vibrational spectroscopic with an ab initio MO study. Particular emphasis is given to the gauche ⇌ anti conformational equilibrium originated by internal rotation about the dithioester SCH2CH3 bond in CH3C(S)SCH2CH3. The ab initio equilibrium geometries of the molecules studied are calculated by gradient geometry refinement, and the conformational dependence of some relevant structural parameters is used to characterize the most important intramolecular interactions present in the various conformers. For ethyl dithioacetate, correlation between the calculated and the observed frequencies for the condensed phases and the isolated molecule clearly shows that the most stable form corresponds to the non-symmetric s-cis/gauche form (the ab initio calculated values of the relevant dihedral angles are 0° (SCSC) and ≈ ±84° (CSCC)). Variable temperature Raman experiments show that the enthalpy difference between the s-cis/gauche and s-cis-anti forms is 1.9 ± 0.2 kJ mol−1. Observed frequency shifts for vSC and vCS are successfully correlated with substitution of the alkyl and acyl fragments. A consistent interpretation of the resonance Raman spectra of both methyl and ethyl dithioacetate and their isotopomers is also achieved.

Comment on “The radical cation of ethyl dithioacetate”

Ab initio MO calculations on the methyl dithioformate system show that the corresponding radical cation has a σ-ground electronic state in contrast with the interpretation recently given by Rhodes (J. Chem. Soc. Chem. Commun. (1988) 1477) from an ESR study on the ethyl dithioacetate radical cation. At the projected UMP2/6-31G * level and corrected for zero-point energy and systematic errors, the two lowest ionization energies of HCSSCH 3 are calculated to be 8.7 (σ) and 9.2 eV (π).

The radical cation of ethyl dithioacetate

In contrast with ester cations (RCO2R) which rearrange spontaneously at 77 K via intramolecular hydrogen atom transfer, stable π-radical cations of ethyl dithioacetate (MeCSSEt+˙) have been observed by e.s.r. spectroscopy, following γ-irradiation of dilute frozen solutions in CFCl3 at 77 K.

ChemInform Abstract: Diastereoselective Auto‐Protonation of Enolates. Anti‐Houk Selectivity.

AbstractMethyl dithioacetate (I) is lithiated to form the enolate (II) which is stereospecifically coupled with the enones (III) to give the enolates (IV).

2-β- d-ribofuranosylbenzoxazole from 2,5-anhydro- d-allonoimidate, and 1,3-dimethyl-8-β- d-ribofuranosylxanthine from 2,5-anhydro- d-allono-thioimidates and -dithioates

The ability of imidates, thioimidates, and dithioates to react with o-aminophenol ( 2) and 5,6-diamino-1,3-dimethyluracil ( 6) was studied, using non-saccharide model compounds, as well as saccharide derivatives. All of the model compounds gave 2-methylbenzoxazole, but only ethyl dithioacetate gave a purine derivative with 6. Methyl 2,5-anhydro- d-allonoimidate hydrochloride reacted with 2 to yield 2-β- d-ribofuranosylbenzoxazole, but failed to react with compound 6. On reaction with compound 6 such fully acylated thioimidates as ethyl and benzyl 2,5-anhydrotri- O-benzoyl- or tri- O- p-toluoyl- d-allonothiomidate hydrochloride yielded amidines that underwent aromatization of the furanose ring. Such monoacylated thioimidates as ethyl or benzyl 2,5-anhydro-6- O-benzoyl-- d-allonothioimidate hydrochloride yielded, with compound 6, 8-(5- O-benzoyl-β- d-ribofuranosyl)-1,3-dimethylxanthine, without aromatization. Such dithioates as benzyl 2,5-anhydro-6- O-benzoyl- d-allonodithioate and ethyl 2,5-anhydrotri- O-benzoyl- d-allonodithioate were obtained by treating the corresponding thioimidate with H 2S in pyridine. With compound 6, the first yielded 8-(5- O-benzoyl-β- d-ribofuranosyl)-1,3-dimethylxanthine, which afforded the free C-nucleoside 1,3-dimethyl-8-β- d-ribofuranosylxanthine on treatment with methanolic ammonia.

ChemInform Abstract: Diastereofacial Selectivity via Aldol Reactions Using Ethyl Dithioacetate and Ethyl Dithiopropionate Enolates.

AbstractThe lithium enolate (III) of the dithioacetate (I) reacts with α‐methyl aldehydes (II) to yield the aldol adducts (IV) + (V) in which the syn configuration of (IV) is favored over the anti configuration of (V).

Diastereofacial selectivity via aldol reactions using ethyl dithioacetate and ethyl dithiopropionate enolates

The lithium enolate of ethyl dithioacetate reacts with α-methyl aldehydes to yield the aldol products in which the syn configuration in the positions β and γ to the thiocarbonyl of the product is favored over the anti configuration. This selectivity is solvent-dependent, and is enhanced at lower temperatures. In most cases, syn:anti product ratios obtained under these conditions varied from 57:43 to >99:1, depending upon the structure of the α-methyl aldehyde. When the lithium enolate of ethyl dithiopropionate was allowed to react with α-methyl aldehydes, only two out of the four possible diastereomers were detected in the product mixtures.

Vibrational spectra and rotational isomerism of simple dialkyl dithioesters and N-acylglycine ethyl dithioesters, thiolesters, and dioxygenesters

Simple dialkyl dithioesters and N-acylglycine ethyl dithioesters have been investigated by Raman, resonance Raman and infrared spectroscopies. Based on the data of isotopic substituted derivatives and a normal coordinate analysis, vibrational assignments have been proposed for methyl dithioacetate. Raman spectra of ethyl dithioacetate(CH 3C(=S)S ▪ CH 2CH 3) and methyl dithiopropionate (CH 3CH 2 ▪ C (=S)SCH 3) have provided fundamental knowledge on rotational isomerism about the bonds indicated. Raman, resonance Raman and FTIR spectroscopic studies on N-acylglycine ethyl dithioesters indicated the coexistence of three conformers in solution and a combined x-ray crystallographic-resonance Raman spectroscopic approach has been used to set up precise structure-spectra correlations for these conformers. The corresponding conformational states of N-acylglycine thiolesters and dioxygenesters are also discussed briefly.

ChemInform Abstract: THE RAMAN AND RESONANCE RAMAN SPECTRA OF SOME SUBSTITUTED DIALKYL DITHIOESTERS AND THEIR ROTATIONAL ISOMERS

The Raman spectra of ethyl dithioacetate, methyl dithiopropionate, and ethyl thionoacetate are presented for the liquid phase at 25 °C and for the solid phase at approximately −130 °C. Certain spec...

ChemInform Abstract: THE INFRARED, RAMAN, AND RESONANCE RAMAN SPECTRA AND NORMAL COORDINATE ANALYSIS OF METHYL AND ETHYL DITHIOACETATE

Infrared, Raman, and resonance Raman data are reported for ethyl and methyl dithioacetate together with data for their isotopically substituted analogs: CD3C(=S)SCH3, CH3C(=S)SCD3, 13CH3C(=S)SCH3, CH313C(=S)SCH3, CD3C(=S)SCH2CH3, CH3C(=S)SCD2CH3, and CH313C(=S)SCH2CH3. Based on these data and a normal coordinate analysis of methyl dithioacetate, assignments are proposed for the majority of bands appearing in the vibrational spectra. Using excitation wavelengths in the 324–356 nm region strong intensity enhancement is observed for Raman bands near 1195, 1100, 730, and 580 cm−1 which are assigned to stretching motions of the CCSSC skeleton. Raman excitation profiles are reported for the 1197 and 581 cm−1 bands of ethyl dithioacetate and the electronic absorbance peak near 305 nm is identified as the source of resonance Raman intensity enhancement.

The infrared, Raman, and resonance Raman spectra and normal coordinate analysis of methyl and ethyl dithioacetate

Infrared, Raman, and resonance Raman data are reported for ethyl and methyl dithioacetate together with data for their isotopically substituted analogs: CD3C(=S)SCH3, CH3C(=S)SCD3, 13CH3C(=S)SCH3, CH313C(=S)SCH3, CD3C(=S)SCH2CH3, CH3C(=S)SCD2CH3, and CH313C(=S)SCH2CH3. Based on these data and a normal coordinate analysis of methyl dithioacetate, assignments are proposed for the majority of bands appearing in the vibrational spectra. Using excitation wavelengths in the 324–356 nm region strong intensity enhancement is observed for Raman bands near 1195, 1100, 730, and 580 cm−1 which are assigned to stretching motions of the CCSSC skeleton. Raman excitation profiles are reported for the 1197 and 581 cm−1 bands of ethyl dithioacetate and the electronic absorbance peak near 305 nm is identified as the source of resonance Raman intensity enhancement.

The Raman and resonance Raman spectra of some substituted dialkyl dithioesters and their rotational isomers

The Raman spectra of ethyl dithioacetate, methyl dithiopropionate, and ethyl thionoacetate are presented for the liquid phase at 25 °C and for the solid phase at approximately −130 °C. Certain spectral features disappear upon going from the liquid to the solid phase allowing the assignment of these bands to rotational isomers which are present in the liquid state only. The consequences of placing a tert-butyl group proximal to the CSS moiety in dithioesters are explored by considering the absorption, Raman, and resonance Raman spectra of ethyl dithiotrimethylacetate and tert-butyl dithioacetate. The resonance Raman spectra of the ionized and unionized forms of dithioacetic acid are also presented. The vibrational spectra of ethyl thiolacetate, and ethyl and methyl thionoacetate are compared to the spectra of the corresponding dithioesters.

Rotational isomers of ethyl dithioacetate and ethyl thionoacetate: A Raman study

AbstractRaman spectra of ethyl dithioacetate (CH3CS2C2H5) and ethyl thionoacetate (CH3C(S)OC2H5) have been measured as a function of temperature in the liquid phase and in the solid phase at low temperature. For both compounds disappearance of several bands from the liquid spectrum on solidification established the presence of more than one conformer in the liquid phase. Temperature variation studies on band pairs whose components belong to different isomers gave enthalpy differences of 598±48 cal mol−1 and 1072±65 cal mol−1 between the conformers of CH3CS2C2H5 and CH3C(S)OC2H5 respectively. The most probable low‐energy conformer, in both instances, is the s‐cis form with all the heavy atoms contained in a single plane.

A Single-step Synthesis of 2-Substituted Benzo-azoles

Abstract 2-Substituted benzimidazoles (3a and 5a), benzothiazoles (3b and 5b), and benzoxazole (3c) are readily synthesized in good yields by treating (thiobenzoylthio)acetic acid (1) or ethyl dithioacetate (4) with the corresponding o-substituted anilines (2a, 2b, and 2c) in slightly alkaline media at room temperature.