Yu. A. Chuvashev

Synthesis of 2-(1-alkoxyvinyl)oxazolidines by condensation of 2-alkoxypropenals with 2-aminoalkanols and ring-chain tautomerism of the products

Reactions of 2-alkoxypropenals with 2-aminoalkanols afforded tautomeric mixtures of previously unknown 2-(1-alkoxyvinyl)oxazolidines and imino alcohols. The condensation takes 2 h at room temperature (89-100%) or 1-5 min under microwave irradiation. The tautomeric equilibrium shifts toward the open-chain structure with increase in the solvent polarity (CDCl3, CD2OD, DMSO-d6, D2O) and temperature. The presence of substituents in the oxazolidine ring raises the stability of the cyclic tautomer.

Reactions of 2-Alkoxypropenals with Thiols in Neutral and Acid Media

Addition of thiols to 2-alkoxypropenal in neutral medium at 20°C in the absence of a catalyst occurs regioselectively, following the Markownikoff pattern. The resulting 2-alkoxy-2-R-thiopropanals are capable of undergoing spontaneous isomerization to 1-alkoxy-1-R-thiopropanones. The addition and isomerization processes are accelerated by heating to 60°C or in the presence of acid catalysts (TsOH, HCl). The reaction is also accompanied by partial disproportionation of 2-oxopropanal O,S-acetals to give O,O- and S,S-acetals.

Synthesis of new 5-substituted hydantoins from 2-alkoxy-1-cyano-1-trimethylsiloxypropenes

Synthetic procedures for preparing previously unknown 5-(1′-alkoxyethylidene)hydantoins from 2-alkoxy-1-cyano-1-trimethylsiloxy-1-(or -2-)propenes by one-pot successive reactions with ethanol and (NH4)2CO3 are developed. Some intermediates, reaction mechanism, and parameters determining the optimal yields are considered. Acid hydrolysis of ethylidenehydantoins occurs at the vinyloxy group and gives 5-acetylhydantoin in 64% yield.

Electrochemical fluorination of benzamide and acetanilide in anhydrous HF and in acetonitrile

Electrochemical fluorination of benzamide in anhydrous hydrogen fluoride does not involve the amide group but occurs exclusively at the aromatic ring, yielding isomeric fluoro- and difluorobenzamides and 3,3,6,6-tetrafluoro-1,4-cyclohexadienecarboxamide. Electrochemical fluorination of benzamide in acetonitrile as solvent gives the same products, as well as benzonitrile and its fluorinated derivatives and products of hydrolysis and fluorination of acetonitrile. Electrochemical fluorination of acetanilide in anhydrous HF leads to complete tarring of the reaction mixture, while its fluorination in acetonitrile results in selective formation of m-fluoroacetanilide.

Kinetics of dimerization of 2-alkylthiopropenals

The rate constants for cyclodimerization of α-alkylthioacroleins were determined. They are two orders of magnitude higher than those for dimerization of α-alkoxyacroleins.

Reaction of α-ethoxyarolein with diethyl malonate

The reaction of α-ethoxyacrolein with diethyl malonate in the presence of EtONa, lithium diisopropylamide, or the Na2CO3−benzene−Et3(PhCH2)NCl catalytic system proceeds as the Michael addition. In the presence of an equimolar amount of triethylamine, selective 1,2-addition followed by dehydration of the 1,2-adduct occurs. Owing to the strong +M effect of the EtO group, α-ethoxyacrolein is a substantially less active Michael acceptor than acrolein.

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).

Synthesis of 2-ethoxyprop-2-enal dimethylhydrazone and its Diels-Alder reactions

Conditions were found for the preparation of 2-ethoxyprop-2-enal dimethylhydrazone by reaction of 2-ethoxypropenal with N,N-dimethylhydrazine. 2-Ethoxyprop-2-enal dimethylhydrazone reacted with methyl vinyl ketone and methyl acrylate according to the [4 + 2]-cycloaddition pattern with regioselective formation of substituted tetrahydropyridines. The major product in the reaction of 2-ethoxyprop-2-enal dimethylhydrazone with 1,4-benzoquinone was 5-hydroxy-1-benzofuran-2-carbaldehyde dimethylhydrazone formed as a result of [3 + 2]-cycloaddition; a small amount of the corresponding [4 + 2]-cycloaddition product was also obtained. Some spontaneous transformations of the primary cycloaddition products were revealed.

Reactions of alcohols with α-alkoxyacroleins at room temperature

The first stage of the reactions of alcohols with α-alkoxyacroleins in an acidic medium at 20°C under kinetically controlled conditions is the Markovnikoff addition at the C=C bond to form 2,2-dialkoxypropanals (methylglyoxal ketals). Under conditions of thermodynamic control, subsequent acetalization of the aldehyde group occurs to form 1,1,2,2-tetraalkoxypropanes. When the duration of the reaction is further increased in the absence of a water acceptor, the ketal group undegroes hydrolysis and methylglyoxal acetals are formed. A method was developed for the preparation of methylglyoxal ketals.

Synthesis of α-alkylthioacroleins

Monomeric α-alkylthioacroleins were obtained by the reaction of alkylthioacetaldehydes with formaldehyde and diethylamine hydrochloride. The structures of the α-alkylthioacroleins were confirmed by NMR spectroscopy and mass spectrometry as well as by chemical transformations of these compounds.