Vol 54, No 12 (2018)

Electron-donor effect of the methyl group in 1,3-dichlorobut-2-ene hampers allylic rearrangement of its primary monochalcogenation products. The use of diphenyl disulfide under harsh conditions (Ph₂S₂–KOH, 1: 10, 75–80°C) makes it possible to obtain a mixture of six bis(phenylsulfanyl)butenes, 1,1-bis(phenylsulfanyl) but-1-ene being the major component. No bis(phenylselanyl) derivatives have been formed on heating up to 80°C. Dipotassium ethane-1,2-dithiolate reacts with 1,3-dichlorobut-2-ene to give a linear product of chlorine substitution at the sp³-carbon atom in two dichlorobutene molecules and a heterocyclic compound, 2-ethylidene-1,4-dithiane (a mixture of E and Z isomers), whose structure is different from the structure of the product obtained from 1,3-dichloropropene under analogous conditions. Mechanisms have been proposed for the formation of the isolated compounds.

Reactions of 2,4-diaryl-1,1,1-trifluorobut-3-yn-2-ols with benzene in the presence of HUSY acidic zeolite (CBV-720) at 100°C in 1 h (glass high-pressure reactor) led to the formation of 1,3-diaryl-1-trifluoromethylindenes in 39–92% yield. A probable reaction mechanism was proposed, which involves formation of the corresponding trifluoromethyl-substituted propargyl cations.

The Knoevenagel condensations of 1H-indole-3-carbaldehyde with various CH acids gave a number of substituted 3-(1H-indol-3-yl)acrylonitriles and acrylamides which were alkylated to afford the corresponding N-alkyl derivatives. The latter were used as Michael acceptors in the synthesis of 4H-pyran, pyridine, 5,6,7,8-tetrahydroquinoline, and [1,3]thiazolo[3,2-a]pyridine derivatives containing an indole fragment.

Base-catalyzed nucleophilic addition of carbon nucleophiles to the exocyclic double bond of 2-(5-aryl-4-methyl-2-oxo-1,2-dihydro-3H-pyrrol-3-ylidene)malononitriles afforded spiro-fused pyrrole derivatives, 7-amino-3-aryl-4-methyl-1-oxo-8-oxa-2-azaspiro[4.5]deca-3,6,9-triene-6-carbonitriles. The products can be regarded as rare structural analogs of biologically active spirans based on isatin.

Regio- and stereoselective methods of synthesis of 3-(pyridin-2-ylsulfanyl)prop-2-enoic acid and alkyl (Z)-3-(pyridin-2-ylsulfanyl)prop-2-enoates have been developed on the basis of nucleophilic addition of pyridine-2-thiol to propynoic acid and alkyl propynoates. Reactions of alkyl (Z)-3-(pyridin-2-ylsulfanyl)prop-2- enoates with methyl iodide afforded 2-[(3-alkoxy-3-oxoprop-1-enyl)sulfanyl]-1-methylpyridinium iodides.

Three-component cascade cyclocondensation of naphthalen-2-amine with cyclic β-dicarbonyl compounds and isoxazole- or isothiazolecarbaldehydes afforded new structural analogs of alkaloids containing isoxazole and isothiazole fragments.

Computer simulation of conformational transformations of 5-methyl-1,3-oxathiane at the DFT PBE/3ζ, RI-MP2/λ2, and HF/6-31++G(d,p) levels of theory has shown that the interconversion between the equatorial (global minimum) and axial chair conformers occurs along several independent pathways through five flexible forms. Nine transition states corresponding to different half-chair forms, as well as symmetrical and unsymmetrical boat conformers, have been localized on the potential energy surface. The free conformational energy of the methyl group has been estimated at 0.9–1.0 kcal/mol by comparison of the calculated and experimental vicinal coupling constants in the ¹H NMR spectra.

The alkylation of 2-(2,6-difluorophenyl)-5-(2-hydroxyphenyl)-1,3,4-oxadiazole with allyl bromide gave 2-(2-allyloxyphenyl)-5-(2,6-difluorophenyl)-1,3,4-oxadiazole, and sulfonylation of the same substrate with benzene- and p-toluenesulfonyl chlorides afforded the corresponding 2-(2-arenesulfonyloxyphenyl)-5-(2,6-difluorophenyl)-1,3,4-oxadiazoles. 2-(2-Allyloxyphenyl)- and 2-(2-tosyloxyphenyl)-5-(2,6-difluorophenyl)- 1,3,4-oxadiazoles showed strong luminescence in the ultraviolet region (λ_max^fl 335–374 nm, φ = 0.12–0.80), whereas the luminescence quantum yield of 2-(2-benzenesulfonyloxyphenyl)-5-(2,6-difluorophenyl)- 1,3,4-oxadiazole was considerably lower (λ_max^fl 334–338 nm, φ = 0.012–0.090).

A synthetic approach to difficultly accessible arenesulfonamides of the azabicycloheptene series through the reaction of cyclopentadiene dimer with 4-chloro-N-(2,2,2-trichloroethylidene)benzenesulfonamide has been demonstrated.

3,3-Dimethyl-2-phenyl-3H-pyrrole reacted with 4-hydroxy-4-methylpent-2-ynenitrile under mild conditions (20–25°C, 5 days) to give (Z)-2-(2,2,7,7-tetramethyl-7a-phenyl-7,7a-dihydropyrrolo[2,1-b]oxazol- 3(2H)-ylidene)acetonitrile in 79% yield with high stereoselectivity.

Methods have been developed for regioselective synthesis of trichloro(1,4-oxathian-2-ylmethyl)-λ⁴- tellane and 1,2-bis(1,4-oxathian-2-ylmethyl)ditellane from tellurium tetrachloride and 2-(allylsulfanyl)ethanol.

New substituted spiro[chromene-4,3′-indoles] and spiro[indole-3,4′-quinolines] have been synthesized in 35–65% yields by one-pot regioselective three-component condensation of N-substituted isatins with two active methylene compounds.

Cyanoethylation of natural glycyrrhetic acid methyl ester gave the corresponding 3β-O-(2-cyanoethyl) derivative which was treated with sodium azide to obtain a novel tetrazolyl derivative of biologically active triterpenoid, methyl 3β-[2-(1H-tetrazol-5-yl)ethoxy]-11-oxoolean-12-en-30-oate.