L. G. Stepanova

Reaction of 2-Alkoxypropenals with 2-Aminoethanethiol and Ring-Chain Tautomerism of the Resulting 2-(1-Alkoxyvinyl)-1,3-thiazolidines

Abstract2-Alkoxypropenals react with 2-aminoethanethiol to give tautomeric mixtures of the corresponding 2-(1-alkoxyvinyl)-1,3-thiazolidines and 2-(2-alkoxy-2-propenylideneamino)ethanethiols in quantitative yield. The state of the ring-chain tautomeric equilibrium depends on the polarity and acidity of the medium and initial reactant ratio, and it does not change on raising the temperature and is only slightly affected by microwave irradiation.

The kinetics and mechanism of cyclodimerization of alkylthiopropenals

The kinetics of 2-alkylthiopropenals cyclodimerization was studied in the temperature range from -7 to +42 °C in heptane and at 20 °C in various solvents. The rate constants for cyclodimerization of 2-alkylthiopropenals are four orders of magnitude higher than those for dimerization of the oxygen-containing analogs, 2-alkoxypropenals, and are independent of the solvent polarity and substituent steric constant. The activation parameters for 2-butylthiopropenal cyclodimerization were estimated. The distribution of electron density in the 2-methoxy- and 2-methylthiopropenals molecules was calculated by the ab initio method. From comparison of the HOMO and LUMO energies for these aldehydes it was concluded that the ratio between the cyclodimerization rates for 2-alkylthio-, 2-ethoxypropenals, and propenal is determined by the HOMO–LUMO gap.

SYNTHESIS AND ANTIMICROBIAL ACTIVITY OF NEW ALDEHYDES AND ACETALS

Methods for the synthesis of new aldehydes and acetals have been developed. The antimicrobial activity of the synthesized compounds against Staphylococcus aureus and Escherichia coli was estimated.

Synthesis of 2,5-bis(butylsulfanyl)-2,3-dihydro-4H-pyran-2-carbaldehyde acetals and their unexpected isomerization

2,5-Bis(alkylsulfanyl)-2,3-dihydro-4H-pyran-2carbaldehydes exhibit bacteriostatic effect [1]. 2,5-Bis(butylsulfanyl)-2,3-dihydro-4H-pyran-2-carbaldehyde is known as a strong and safe antiseptic [2]. We examined its reactions with alcohols in order to obtain new potential biologically active derivatives. Unlike 2,5-dialkoxy-2,3-dihydro-4H-pyran-2-carbaldehydes [3] which take up alcohols at the endocyclic double bond, the reaction of sulfur-containing analog I with alcohols in acid medium at room temperature (i.e., under comparable conditions) occurred at the carbonyl group. However, apart from the expected symmetric dialkyl acetal II, diastereoisomeric mixed acetals III and IV were always formed, regardless of the acid taken as catalyst (p-TsOH, HClO4, CF3COOH) or alcohol (MeOH, EtOH); the products are readily detected by gas chromatography–mass spectrometry. To determine the product structure, isomer mixture obtained in the reaction of aldehyde I with methanol were separated by high-performance liquid chromatography (HPLC). The reaction with methanol was selected as model process, taking into account more facile identification of methyl derivatives by NMR spectroscopy. Judging by the intensities of signals from the acetal CH protons at δ 4.27 (IIa), 4.53 (IIIa), and 4.47 ppm (IVa) in the H NMR spectra, the product ratio changed from 2 : 1 : 1 to 1 : 1 : (1–2) in 7–10 days, the conversion of the initial aldehyde being 80–100%. Analysis of the H and C NMR spectra of the first isomer allowed us to identify it as symmetric dimethyl acetal IIa. Formalistically, two other isomers IIIa and IVa result from exchange of OMe and SBu groups in the vicinal acetal and hemithioketal moieties (at the C and C atoms).

Reaction of ?-alkoxyacroleins with thiols

ConclusionsThe nucleophilic or radical addition of thiols to α-alkoxyacroleins leads to 2-alkoxy-3-organylthiopropanals. Depending on the reaction conditions, the product of the electrophilic reaction of the same reagents is a 2-alkoxy-2-organylthiopropanal or 1-alkoxy-1-organylthiopropanone.

Hydrolysis of β-ethylthiocrotonaldehyde diethyl acetal

Conclusions1.Depending on the reaction conditions, the hydrolysis ofβ-ethylthiocrotonaldehyde diethyl acetal leads either toβ-ethylthiocrotonaldehyde or to methylβ-ethylthiovinyl ketone.2.The 2,4-dinitrophenylhydrazones ofβ-ethylthiocrotonaldehyde and methylβ-ethylthiovinyl ketone when heated in an acid medium are respectively converted to the 5-methyl and 5-methyl derivatives of 1-(2,4-dinitrophenyl)pyrazole.

Reaction of tetraethoxysilane and triethoxymethane with some α-substituted α, β-unsaturated aldehydes

1. The reaction of α-halo-substituted α, β-unsaturated aldehydes with tetraethoxysilane and triethoxy-methane makes it possible to obtain their acetals in good yields. 2. The reaction of α-ethoxyacrolein with tetraethoxysilane and with triethoxymethane does not give the acetal, but instead either 2, 2-diethoxypropanal or 1,1,2,2,4,4-hexaethoxybutane.

Electrophilic addition to 2-formyl-2,5-dialkoxy-2, 3-dihydro-γ-pyrans

It is shown that polarization of the endocyclic double bond in the electrophilic addition of alcohols and water to 2-formyl-2,5-dialkoxy-2,3-dihydro-γ-pyrans is directed toward the carbon atom in the 6 position.

β-Alkylthio-substituted α, β-unsaturated aldehydes

1. The reaction of sodium alkanethiolates with the acetals of α-halo-substituted α, β-unsaturated aldehydes leads to the correspondingβ-alkylthio-substituted derivative independent of the nature of the halogen or of the presence of an alkyl group in theβ position, and also independent of the character of the employed solvent. 2. In acid medium theβ-alkylthio-substituted acetals ofα, β-unsaturated aldehydes are hydrolyzed at room temperature without cleaving the C-S linkage to give the correspondingβ-alkylthio-substitutedα, β-unsaturated aldehydes. The latter under mild conditions form derivatives at the carbonyl group without changing the carbon skeleton. This reaction when run with heating leads to cyclization and the formation of pyrazole derivatives. Prolonged heating of the butylthioacrolein with excess butanethiol leads to the reaction product at the two reaction centers, and specifically to 1,1,3,3-tetrabutylthiopropane.