Arylacetylenes readily react with aromatic aldazines in temperature to afford mainly 4-arylmethyl-3,5-diaryl-1Hpyrazoles in up to 47% yield along with minor amounts of 1-arylmethyl-3,5-diaryl-1H-pyrazoles and 1,2-diaryl-1,2bis(3,5-diaryl-1H-pyrazol-1-yl)ethanes. The reaction is rationalized as proceeding via the diazaallyl anions, the adducts of acetylenic carbanions to a C=N bond, which further undergo the proton transfer processes and intramolecular cyclization to the above pyrazole derivatives.

Pharmaceutically prospective 2-substituted-4,5-dimethyloxazoles are synthesized in 16-58% yield via cascade assembly of one molecule of primary amide with two molecules of acetylene gas in the KOH/MeOH/DMSO catalytic triad (90 degrees C, 2 h). This self-organization of oxazoles demonstrates unexpected successful competition with the alkaline hydrolysis of amides. The mechanism involving amide N-vinylation, enamine-imine isomerization, imine ethynylation and intramolecular O-vinylation cascade sequence has been deduced and supported by quantum-chemical calculations using the B2PLYP-D3/6-311+G**//B3LYP/6-31+G*+IEF PCM (B3LYP/6-31+G*) approach.

Secondary phosphine selenides were found to react with γ-aminoacetylenic ketones (80-85 °C, MeCN, 17-40 h) to afford 1,2-dihydro-3H-pyrrole-3-selones in 48-80% yields, products of unprecedented selenium transfer from the P═Se bond to replace the carbonyl oxygen and to form dihydro-3H-pyrrole-3-selones having a C═Se bond stable under ambient conditions.

Di(het)aryldiynes smoothly react with N-benzylaldimines in a [4 + 3] cycloaddition manner under the action of the KOBut/DMSO system (60 °C, 30 min) to afford pharmaceutically relevant tetra(het)arylsubstituted 3H-azepines in up to 71% yield. The process involves the addition of azaallyl anions to one of the triple bonds of diynes followed by prototropic isomerization and cyclization of anionic intermediates with participation of the second triple bond. The cascade mechanism is consistent with quantum-chemical analysis (B2PLYP-D3/6-311+G**//B3LYP-D3/6-31+G* + PCM).

Structurally analogous C- and N-linked 1,4-bis(imino)-functionalized benzenes react with acetylenes in the KOBut/ DMSO superbase system to give the corresponding bis-(propargylamino)-containing derivatives in 62–82% yields (C-linking) or 38–42% yields (N-linking). In the latter case, with phenylacetylene, the yields of mono- and bisadducts were 32 and 38%, respectively. The observed dissimilarities between both bisimine chemotypes in the reactivity and synthetic outcomes imply the long-range adverse repulsive interaction between nitrogen anionic center and the second nitrogen atom in the N-linked 1,4-bis(imino) benzenes.

An efficient one-pot synthesis of 1,2,5-trisubstituted-1,2-dihydro-3H-pyrrole-3-thiones (up to 91% yield), representatives of essentially new heterocyclic systems, by the successive treatment of available propargylamines with acyl chlorides (PdCl2/CuI/Ph3P/Et3N, toluene, 40-45 °C, 3 h) and sodium sulfide (Na2S·9H2O, EtOH, 20-25 °C, 7 h) has been developed. The synthesis comprises the addition of sulfide anions to the formed aminoacetylenic ketones followed by dehydrative cyclization of the prototropically rearranged adducts.

By using a quantum-chemical approach, B2PLYP-D2/6-311+G**//B3LYP/6-31+G*, we have carried out a detailed study of the assembly of 1-pyrrolines from N-benzyl-1-phenylmethanimine and phenylacetylene in the superbasic medium KOtBu/dimethyl sulfoxide (DMSO). In this way, we have considered, both theoretically and experimentally, the mechanisms of the assembly through a concerted and stepwise nucleophilic cycloaddition and have addressed the side processes accompanying the assembly. It is found that the assembly via the concerted cycloaddition is kinetically more favorable than that via the stepwise cycloaddition. At the same time, the reaction of C-vinylation of aldimine with phenylacetylene occurs with a similar activation energy as the concerted cycloaddition and leads to the formation of 2-aza-1,4-pentadiene. The anion of 2-aza-1,4-pentadiene is an intermediate for the side processes leading to the formation of triarylpyridines and 1,3-diarylpropan-1-ones. Triarylpyridines are formed through the concerted cycloaddition of the next phenylacetylene molecule to 2-aza-1,4-pentadiene, while 1,3-diarylpropan-1-ones are formed as a result of the hydrolysis of 2-aza-1,4-pentadienes. It is found out that the mild conditions for the assembly of 1-pyrrolines (60 °C, 15 min) relate to the formation of complexes in the KOtBu/DMSO superbasic medium, where the anion is readily accessible for the nucleophilic attack by the phenylacetylene molecule.

N-Benzyl aldimines react with arylacetylenes in the presence of ButOK/DMSO superbase system to afford 2,3,5-triaryl-1-pyrrolines as two tautomers with 1,2- and 1,5-location of the double bond, both being the trans-diastereomers. This version of the C=N bond ethynylation differs from the previous one with N-benzyl ketimines. The oxidation of the pyrroline tautomeric mixtures without their isolation gives 2,3,5-triaryl-1H-pyrroles.

Pd/Cu-catalyzed cross-coupling of propargylamines with aromatic acyl chlorides (PdCl2, CuI, Ph3P, 40-45 degrees C) provides alpha-aryl(hetaryl)aminoacetylenic ketones in a yield of up to 97%. The latter undergo cyclization to 1,2,5-triaryl(hetaryl)-1,2-dihydro-3H-pyrrol-3-ones in up to 93% yield after the treatment with KOH or Et2NH (40-55 degrees C, aqueous ethanol). The one-pot synthesis of the pyrrol-3-ones (in up to 62% yields) by consecutive treatment of the above propargylamines with acyl chlorides (PdCl2/CuI/Ph3P) and a base (KOH) in aqueous ethanol has been also developed.

2-Acetyl-3,4-dihydropyrans, assembled from acetylene gas and ketones in a one-pot procedure, are ethynylated with acetylenes (KOBut/DMSO, 15 °C, 2 h) to give acetylenic alcohols, which readily cyclize (TFA, rt, 5 min) to 7-ethynyl-6,8-dioxabicyclo[3.2.1]octanes in up to 92% yield. The ring closure of the above acetylenic alcohols can be performed without their isolation from the reaction mixture. Thus, the synthesis of 7-ethynyl-6,8-dioxabicyclo[3.2.1]octanes can be realized in just two synthetic operations from simple and available starting materials under mild transition-metal-free conditions.

Semistabilized diazatrienyl anions are generated by the reaction of 2-pyridylarylimines with arylacetylenes in superbase systems MOtBu (M = Li, Na, K)/DMSO at ambient temperature for 15 min. The initial intermediate N-centered propargyl-1,3-diaza-1,3,5-trienyl anions undergo intermolecular cyclization to benzyl imidazopyridine anions (formally [3 + 2] cycloaddition), further intercepting a second molecule of the starting pyridylimines or a proton of medium to afford (Z)-stilbene/imidazopyridine ensembles and benzyl imidazopyridines. The charge distribution in all intermediate anions and their synthetic evolution are consistent with quantum-chemical analysis (B2PLYPD/6-311+G**//B3LYP/6-31+G*).

The photochemical 6 pi-electrocyclization of diarylethenes (DAE), 2-vinylbiaryls (VBA) and their derivatives is widely used in organic synthesis. Combination of these motifs in one molecule opens the issue of selectivity of the photochemical reaction. We have found that upon UV irradiation, 3-(1,2-diarylvinyl)-2-arylimidazo[1,2-a]pyridines comprising both DAE and VBA moieties form products of VBA cyclization followed by oxidation. The selectivity of the process was rationalized by DFT calculations. The presented reaction gave access to highly fluorescent 5,6-diarylnaphtho[1 ',2 ':4,5]imidazo[1,2-a]pyridine derivatives.

1-(4-Chlorophenyl)-2-methyl-2-phenyl-5-(thiophen-2-yl)-1,2-dihydro-3H-pyrrol-3-one, was synthesized for the first time in 75% yield by the base-catalyzed intramolecular cyclization of 4-((4-chlorophenyl)amino)-4-phenyl-1-(thiophen-2-yl)pent-2-yn-1-one. The starting aminoacetylenic ketone was prepared by cross-coupling of available propargylamines with acyl chlorides in the presence of the PdCl2/CuI/Ph3P catalytic system.

N-Benzyl ketimines undergo [3 + 2] cycloaddition with arylacetylenes in the KOBut/DMSO solution to 2,3,5-triarylpyrrolines, which are oxidized (chloranil, DDQ) in situ to 2,3,5-triaryl-2H-pyrroles in 53-71% yields. The intermediate 1-pyrrolines can be isolated in 31-91% yields and separately oxidized to the corresponding 2H-pyrroles.

A new superbase-promoted reaction of acetylene involves self-organization of its three molecules with one molecule of arylamine in KOH/DMSO system to afford 1-aryl-2,5- dimethylpyrroles in up to 63% yields. The key step of this reaction cascade is assumed to be the nucleophilic addition of acetylene to the C = N bond of the intermediate aldimine (aza-Favorsky reaction).

Several imines, readily derived from aryl methyl ketones and benzylamines, react with acetylene gas in KOBut/DMSO system to afford 2-azadienes stereoselectively. This new C-C bond constructing reaction involves, instead of the expected ethynylation of the C═N bond, the addition of azaallyl anions to the triple bond of acetylene.

Aldimines react with aryl- and hetarylacetylenes in the presence of KOBut/dimethyl sulfoxide (DMSO) or NaOBut/DMSO systems under exceptionally mild conditions (14 °C, 1 h) to afford C-H-vinylated products, 1-azadienes of E configuration relative to the C-C bond, in up to 72% yield. Vinylation involves the unprecedentedly fast multiposition proton transfer in the intermediate adducts of acetylene to the C═N bond. This new Csp2-Csp2 bond-forming reaction opens a straightforward pot-, atom-, step-, and energy-economic access to synthetically valuable 1-azadienes.

The head‐to‐tail autocondensation of 4‐fluoroacetophenone in the KOH/DMSO superbase suspension stops on dimerization step affording 4‐acetylbenzyl‐4'‐fluorophenylketone in 96 % yield. Further condensation of the diketone formed is prevented by a weaker electron‐withdrawing effect of enolate spacer, –CH=C(OK)–. 2‐Fluoro‐ and 3‐fluoroacetophenones are inactive in this reaction. Other superbases of the type MOR/DMSO (M = Na, K; R = H, OBut) are inferior in promotion of this reaction providing 71–76 % yields of the dimeric ketone. Other weak acids like non‐fluorinated acylbenzenes prove to be also capable of forming Csp2–Csp3 bond with 4‐fluoroacetophenone under similar conditions. This new group of fluorine substitution (SNAr) reaction opens a short and simple route to so far inaccessible aromatic diketones via the nucleophilic substitution of fluorine atom in 4‐fluoroacetophenone by available acylbenzenes. The quantum‐chemical rationale of the observed substitution process as competing with aldol condensation is suggested.

A new Csp3–Csp bond forming reaction is reported: the C=N bond of widespread imines reacts with acetylene gas in the presence of superbase KOtBu/DMSO at room temperature to afford terminal α‐aminoacetylenes in up to 94 % yield. The reaction allows nitrogen heterocycles, e.g. 3H‐indoles, to be directly cross‐coupled with acetylene gas.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.