Vol 55, No 11 (2019)

The review presents an analysis of the recent literature on the use of copper catalysis in the formation of a C-S bond between aryl halides and thiols. The review covers the use of ligand-free systems, water as a solvent, and recyclable catalysts.

The acid-catalyzed reaction of C⁴-methyl derivatives of levoglucosenone with ethanethiol and propane-1,3-dithiol was studied. The reaction takes a nontrivial route and involves intramolecular oxacyclization to form 2,5-dihydrofurans containing a thioacetal group at C⁵ in the side chain. The transformation provides a short way to synthesize chiral 2,5,5-trialkyl-substituted 2,5-dihydrofurans from levoglucosenone.

3,4-Dihydropyrimidines obtained by the Biginelli reaction react with hydrazine to give a mixture of N-[(3,5-dimethyl-1H-pyrazol-4-yl)(R)methyl]ureas and 4-R-3,7a-dimethyl-1,3a,4,5,7,7a-hexahydro-6H-pyrazolo[3,4-d]pyrimidin-6-ones. The latter transform into N-[(3,5-dimethyl-1H-pyrazol-4-yl)(R)methyl]ureas in an acidic medium.

4,4′-Bis[4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)phenylcarbonylamino]-3,3′-dichlorodiphenylme-thane has been obtained by the reaction of 4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)benzoyl chloride with 4,4′-diamino-3,3′-dichlorodiphenylmethane. 1,4-Bis[2-(4-aminophenylcarbonyloxy)ethoxy]benzene has been prepared by the reaction of potassium 4-aminobenzoate with 1,4-bis(2-chloroethoxy)benzene. The synthesized diamine has been reacted with maleic anhydride to obtain 1,4-bis[4-(2-carboxyethen-1-ylcarbamoyl)phenyl-carbonyloxyethoxyjbenzene, whose subsequent cyclization with acetic anhydride gave 1,4-bis{2-[4-(2,5-dioxo-2,5-dihydro-1H-pyrrol-1-yl)-phenylcarbonyloxy]ethoxy}benzene.

The reactions of 4-methyl- and (RS)-4,6-dimethyl-2-phenyl-5,6-dihydrobenzo[4′,5′]imidazo-[2′,1′:6,1]pyrido[2,3-d]pyrimidines and 4-methyl-5,6-dihydrobenzo[4′,5′]imidazo[2′,1:6,l]pyrido[2,3-d]pyrimi-din-2-ol with aromatic and heterocyclic aldehydes under various experimental conditions were studied. It was shown that the reaction with aldehydes upon boiling in acetic anhydride involves exclusively the 6-methylene group in the a-position to the benzimidazole fragment of the tetracycle and is accompanied by a 1,3-prototropic shift, which results in the formation of 6-aryl(hetaryl)methyl-4-methyl derivatives. The 4-methyl group in the substituted 2-phenyl(hydroxy)derivatives of 5,6-dihydrobenzo[4′,5′]imidazo[2′,1′:6,1]pyrido[2,3-d]pyrimidines reacts with aldehydes only under fusion conditions in the presence of ZnCl₂. The structure of the synthesized compounds was confirmed by one- and two-dimensional (NOESY) ¹H NMR spectroscopy and XRD analysis.

The reaction of hydrazides of alicyclic capric and aromatic benzoic and p-hydroxybenzoic acids with the peroxide product of non-1-ene ozonolysis was studied. Capric acid hydrazide exhibits the strongest reducing properties in aprotic solvents (methylene chloride, THF) and leads to chemoselective and high-yield (~ 80%) formation of the corresponding acylhydrazone. p-Hydroxybenzoic acid hydrazide forms a similar derivative with a yield of 67% only in THF.

The reaction of 2-bromopropanoyl chloride with lithium ethyl acetate generated in situ by the reaction of equimolar amounts of lithium diisopropylamide with ethyl acetate forms, depending on the conditions (temperature, time, reagent ratio), diethyl 2,2′-(3-methyloxirane-2,2-diyl)diacetate, 2,2-dibromo-N,N-diisopropylpropanamide, and ethyl (5-methyl-4-oxo-4,5-dihydrofuran-2-yl)acetate as minor by-products along with the expected acylation product ethyl 4-bromo-3-oxopentanoate. The reaction with 2 or 5 equiv of lithium ethyl acetate (–78°C → –20°C) gave, together with the mentioned α-bromo ester, ethyl (5-methyl-4-oxo-4,5-dihydrofuran-2-yl)acetate formed as a result of transformations of the adduct of the second LiCH₂CO₂Et molecule and ethyl-4-bromo-3-oxopentanoate. The reaction 2-bromopropanoyl chloride with sodium malonic ester involves acylation of enol form of the primary expected acylation product to afford dimethyl |2-bromo-1-[(2-bromopropanoyl)oxy]propylidene-malonate.

Ozonolysis of 3β,28-diacyloxylup-20,29-enes gave 20-oxo-29-nor-3β,28-diacyloxylup-20,29-enes, which were brominated with molecular bromine in AcOH to obtain a mixture of 30-bromo- and 30-dibromo derivatives. Ozonolysis of 30-bromo-3β,28-diacylbetulin produced 29-nor-30-bromoketones, whose reaction with sodium azide afforded 29-nor-30-azidoketones of the lupane series.

N-Substituted succinimides having different alkyl groups were prepared by the reaction of N-substituted maleimide with aldehydes. A two-component catalyst system composed of an amino acid (l-isoleucine) and a base (KOH) was used to facilitate reaction of the α-hydrogen-containing aldehyde with N-substituted maleimide. With 20 mol % catalyst/cocatalyst, good results in term of the reaction time and yield (892-99%) of products containing contiguous quaternary and tertiary stereogenic centers were obtained. The CHN elemental analyses of N-substituted succinimides indicated appreciable purity. Structural assessment of the synthesized N-substituted succinimides was carried out by ¹H and ¹³C NMR spectroscopy. The products exhibited excellent antioxidant and mild antimicrobial activities.

The O-triethylsilylated hemiaminal Et₃SiOCH₂NMe₂ readily transfers the Me₂NCH₂-group to various thioureas under mild conditions and without catalysts or co-reagents. In the reaction with PhNHC(=S)·NHPh, the initially formed mono-substituted derivative PhNHC(=S)NPhCH₂NMe₂ readily rearranges to produce the unsymmetrical thiourea PhNHC(=S)NMe₂ and hexahydro-1,3,5-triphenyl-1,3,5-triazine.

A novel magnetic Co nanoparticle catalyst was prepared by coating Fe₃0₄magnetic nanoparticles with tetraethyl orthosilicate functionalized with (3-chloropropyl)trimethoxysilane and 2-amino-5-mercapto-1,3,4-thiadiazole ligands followed by complexation with Co(OAc)₄. The catalyst was then characterized and applied for the synthesis of various tetrazoles by the reactions of amines with sodium azide and triethyl orthoformate in solvent-free conditions at 100°C.

A novel one-pot approach has been developed for a high-yield synthesis of 4-phenyl-4H-pyran derivatives by the three-component condensation of dimethyl 3-oxopentanedioate or 3-oxo-3-arylpropanoic acid esters, aldehydes, with malononitrile in the presence of a DIPEA catalyst in ethanol at room temperature. The significant features of the present strategy include efficiency, high yield, inexpensive catalyst, mild reaction conditions, and simple purification procedure.

The reaction of 1,4-dichlorobut-2-yne with propane-1,3-dithiolate was carried out for the first time. A mixture of cyclic (2-vinyl-1,4-dithiepan-2-ene) and linear (5,10-dithiatridec-1,12-diyne-3,10-diene) products was synthesized, in 30 and 15% yields, respectively.

Novel derivatives of 2-imino-2,5-dihydrofuran-3-carboxamides containing a thiourea residue have been synthesized by the reaction of 2-imino-2,5-dihydrofuran-3-carboxamides with thiosemicarbazide in glacial acetic acid. The synthesized N-substituted iminodihydrofurans have been condensed with ethyl chloroacetate to obtain novel derivatives of iminodihydrofurans containing an oxothiazolidinylidene ring. These methods open up new synthetic approaches to previously unknown systems containing iminodihydrofuran, thiourea and oxothiazolidinylidene fragments.