RESUMEN
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.
RESUMEN
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.
RESUMEN
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.
RESUMEN
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*).
RESUMEN
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 CâN bond. This new Csp2-Csp2 bond-forming reaction opens a straightforward pot-, atom-, step-, and energy-economic access to synthetically valuable 1-azadienes.
RESUMEN
Ketones with bulky aromatic, heteroaromatic and ferrocene substituents react with acetylene in the presence of a KOH/DMSO super-base suspension (90 °C, 15â min) to give polysubstituted furans in up to 86 % isolated yields in a one-pot fashion. This assembly of the furan scaffold involves a domino sequence in which one molecule of ketone reacts with two molecules of acetylene.
RESUMEN
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).
RESUMEN
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.
RESUMEN
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 CâN bond, the addition of azaallyl anions to the triple bond of acetylene.
RESUMEN
The products of the one-pot assembly of acetylene and ketones in the KOH/DMSO system, 7-methylene-6,8-dioxabicyclo[3.2.1]octanes, undergo an acid-catalyzed (CF3COOH, room temperature) rearrangement to rarely substituted cyclopentadienes in good-to-excellent yields. The mechanism of the rearrangement has been supported by the isolation and corresponding transformations of two intermediates.
RESUMEN
Acetylene reacts with methylaryl(hetaryl)ketones in the presence of 6.5 mol % KOH in DMSO to give diastereoselectively in single operationally functionalized cyclopentenes. This domino cyclization involving two molecules of acetylene and two molecules of ketone proceeds with the formation of four C-C bonds. The complementary assembly of the cyclopentenes with similar functionalities from acetylenes and 1,5-diketones has been developed.