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In this study, 2H-1,1,3,4,4-pentachloro-1,3-butadiene (1) was reacted with different thiols (2-methyl-2-propanethiol 2a, benzyl mercaptan 2b, 4-tert-butylbenzenethiol 2c, 4-nitrothiophenol 2d) in ethanol in the presence of NaOH to afford mono-thio-substituted-1,3-butadienes and mono-and tris-thio-substituted-1-buten-3-ynes. Among them, (4-tert-butylphenyl)(1,3,4,4-tetrachlorobuta-1,3-dienyl)sulfane (4c) exhibited two isomers of mono products. Moreover, the reaction of compound (1) with 2-hydroxythiophenol (2e) in dimethylformamide in the presence of triethylamine took place the formation of OH-protected butadiene structure 2-((Z)-1,3,4,4-tetrachlorobuta-1,3-dienylthio)phenol (4e) and ring-closed butadiene structure (E)-2-(2,3,3-trichloroallylidene)benzo[d][1,3]oxathiole (6), together and with two isomers of each. Their structures identified on the basis of GC-MS(+EI) analysis with different retention times (RT). Characterization of the synthesized compounds was done using several methods, mass spectrometry (GC-MS(+EI)),1H-,13C-, APT-NMR, FTIR and elemental analysis. © 2019, Turkish Chemical Society. All rights reserved. Istanbul Üniversitesi: NP-42986 This study was funded by Istanbul University with the project number (NP-42986). I thank the Research Fund of Istanbul University – Cerrahpasa for financial help.

Readily available tetrachloro-2-aza-1,3-butadienes enter into directed cyclocondensation reaction with N-phenyl-1,2-cyclopentanediamine which leads to regioselective cyclopentane annulation by the 1,3,5-triazepine. The formation of the 1,3,5-triazepine derivatives was confirmed proved by 1H- and 13C-NMR spectral study, elemental analysis and, in one case, single-crystal x-ray crystallographic study.

A convenient and efficient procedure for the preparation of 3,4-dihydro-2H-pyran derivatives containing a sugar moiety is described. The reaction sequence is: Knoevenagel condensation of unprotected sugars and CH acids, acetylation of C-glycosides and hetero-Diels–Alder reaction. O-Acetylated 1,3-dimethyl-2,4,6-trioxo-pyrimidin-5-ylidene derivatives were used as new heterodienes in the synthesis of fused uracils—pyrano[2,3-d]pyrimidines with a sugar moiety. Solvent-free hetero-Diels–Alder cycloadditions of O-acetylated pyrimidin-5-ylidene alditols with enol ethers and cyclic enol ether were investigated at room temperature. New, enantiomerically pure cis and trans diastereoisomers of pyrano[2,3-d]pyrimidines and cis–cis, trans–cis diastereoisomers of pyrano[3′,2′:5,6]pyrano[2,3-d]pyrimidines with alditol moiety were obtained. The same pyrimidin-5-ylidene alditols underwent conjugate Michael addition–cyclizations with malononitrile at room temperature to afford optically active diastereoisomers of pyrano[2,3-d]pyrimidine-6-carbonitriles with a sugar moiety.

Diels-Alder reactions of a range of 1-(alkoxy/alkyl-substituted phenyl)buta-1,3-dienes with methyl vinyl ketone and methyl acrylate carried out in ethanol as the reaction medium under 9 kbar pressure were investigated. The use of high pressure as the activating method of the Diels-Alder reactions allows the efficient and endodiastereoselective generation of a series of cis-cyclohexenyl-benzene cycloadducts, which are selectively converted into their trans-epimers. The cis-cyclohexenyl-benzenes and trans-cyclohexenyl-benzenes produced are useful precursors for accessing substituted privileged cis-6a,7,8,10a-tetrahydro-6H-benzo[c]chromene and trans-6a,7,8,10a-tetrahydro-6H-benzo[c]chromene skeletons. The total syntheses of Δ(9)-cis-tetrahydrocannabinol (THC) and Δ(9)-trans-THC, through the use of selected Diels-Alder adducts, are described. Finally, a route for obtaining Δ(9)-trans-THC in both enantiomeric pure forms based on the (S)-(-)-1-amino-2-(methoxymethyl)pyrrolidine (SAMP)-hydrazone method is also reported.

Diversely functionalized imidazole-4-carboxylates were synthesized by microwave-assisted 1,5-eletrocyclization of 1,2-diaza-1,3-diene-derived azavinyl azomethine ylides. 1,2-Diaza-1,3-dienes were treated with primary aliphatic or aromatic amines and subjected to microwave irradiation in the presence of aldehydes. 3-Alkyl- and 3-arylimidazole-4-carboxylates were prepared in good yields through a one-pot multicomponent procedure. Modulation of the substituents at C-2, N-3, and C-5 was possible, and 2-unsubstituted imidazoles were obtained when paraformaldehyde was used.

The substitution of the aryl group at trans position with respect to the N atom in the imine part of 4,4-dihalogeno-1,1-aryl-2-aza­buta-1,3-dienes [Ar2C=N—C(H)=CX 2] by a CN group allows to get an almost perfectly planar mol­ecule., The title compound, C12H10Br2N2O2, represents an example of a planar π-con­jugated 2-aza­butadiene mol­ecule, which is both an inter­esting starting material for further organic transformations and a potential ligand in organometallic coordination chemistry. Its metric mol­ecular parameters are typical for the family of 2-aza­buta-1,3-dienes not substituted at the (CH) 3-position. In the crystal, the almost planar (r.m.s. deviation = 0.0658 Å) aza­diene mol­ecules form one-dimensional double-wide ribbons through inter­molecular halogen bonds (C—Br⋯O and C—Br⋯Br—C), which then stack in a slipped manner through weak C—H⋯Br and π–π inter­actions to generate a three-dimensional network.

Inverse-electron demand Diels–Alder cycloadditions of sterically hindered cycloalkylidene derivatives of benzoylacetonitrile and N,N′-dimethylbarbituric acid with enol ethers, cyclic enol ethers and also sterically hindered cycloalkylidenecycloalkanes were investigated. New spiro, dispirodihydropyrans, spirouracils, and dispirouracils were obtained. To confirm the experimental results, frontier orbital HOMO and LUMO energies of heterodienes and dienophiles were calculated by semi-empirical AM1, PM3 methods and ab initio Hartree–Fock calculations.

The reaction of 1,2-diaza-1,3-butadienes with dialkyl phenylphosphonites under solvent-free conditions proceeds via zwitterionic intermediate and gives, by precipitation, the stable ylidic α-phosphanylidene-hydrazones that, in turn, can be transformed into the corresponding 3-phenyl-2 H -1,2,3λ 5 -diazaphospholes. The latter compounds are converted by hydrolytic cleavage in methanol–water (95:5) into E -hydrazonophosphonates that are useful for the preparation of the corresponding β-ketophosphonates and 4-[alkoxy(phenyl)phosphoryl]-1,2-diaza-1,3-butadienes. These peculiar 1,2-diaza-1,3-butadienes, bearing an alkoxy(phenyl)phosphoryl group on the carbon atom in position 4 are also able to add different nucleophiles, such as methanol or thiourea, giving 2-[alkoxy(phenyl)phosphoryl]-2-methoxyhydrazones and 5-phosphinate-substituted thiazol-4-ones, respectively.

Michael-type addition of aziridinecarboxylates to 1,2-diaza-1,3-butadienes under solvent-free conditions (SFC) resulted in the formation of r-aziridinohydrazone adducts. In toluene under reflux, r-aziridinohydrazones gave imidazoles in moderate to good yields. Such a reactivity pattern is explained by 1,5-electrocyclization of azavinyl azomethine ylide generated through thermal ring opening of r-aziridinohydrazones. In the charming panorama of ylides, azomethine ylides represent a particular case of useful intermediates in organic synthesis. Based on his pioneer studies, in 1963 Huisgen disclosed the existence of 1,3-dipoles and opened the route to 1,3-dipolar cycloadditions. 1 Both intra- and intermolecular 1,3-dipolar cycloadditions of simple azomethine ylides with dipolarophiles lead to five-membered heterocycles containing one nitrogen atom, namely pyrrolidine or pyrroline derivatives (Figure 1, eq 1). 2 When a double bond or a 1,3-diene system is conjugated with the azomethine ylide, five(pyrroline) or seven-membered (dihydroazepine) heterocycles can be obtained by 1,5- or 1,7-electrocyclization, respectively (Figure 1, eqs 2 and 3). 3

[structures: see text] The present article describes the reaction between 1,2-diaza-1,3-butadienes and trialkyl phosphites, under an atmosphere of nitrogen and under solvent-free conditions, to give alkyl 3,3-dialkoxy-2H-1,2,3lambda5-diazaphosphole-4-carboxylates that, in turn, are converted into corresponding E-hydrazonophosphonates by treatment with THF:water (95:5). These latter compounds are obtained directly by the reaction of 1,2-diaza-1,3-butadienes with trialkyl phosphites in the presence of air. These compounds are useful for the further preparation of dialkyl (5-methyl-3-oxo-2,3-dihydro-1H-4-pyrazolyl)phosphonates and 2-dialkoxyphosphoryl-1,2,3-thiadiazoles.