The mechanisms of fundamental base‐promoted acetylene reactions, namely, nucleophilic addition to the triple C ≡ C bond (vinylation) and nucleophilic addition of acetylenic carbanion to a carbonyl group (ethynylation), are addressed using three models of different complexity—pentasolvate, monosolvate, and anionic—which describe the catalytic superbasic systems MOH(OBut)/DMSO (suspensions of alkali hydroxides or tert‐butoxides in dimethyl sulfoxide). The above acetylene reactions and sequential transformations of reagents arranged by the superbasic center are modeled within the framework of the most complete pentasolvate model, in which the superbase is represented by the KOH·5DMSO (KOBut·5DMSO) complexes. We have developed approaches to the construction of simplified models (monosolvate and anionic) to describe transformations in complex systems. The mechanisms of cascade assemblies of 6,8‐dioxabicyclo[3.2.1]octanes, cyclopentenones, and furan cycles from ketones and acetylenes in the superbasic environment are investigated using a uniform B2PLYP/6‐311+G**//B3LYP/6‐31+G* approach, and the energy profiles of these different carbo‐ and heterocycles are analyzed.

A rapidly developing approach adding new dimensions to acetylene chemistry relying on employment of high basicity media such as alkali metal hydroxide suspensions in dimethyl sulfoxide (DMSO) has been, for the first time, investigated theoretically using ab initio models. Extending our recently introduced model of superbase catalysis with a nondissociated KOH (or NaOH) participation, we present here a model for a superbasic reaction center with the first solvation shell explicitly included. The alkali metal hydroxides in a DMSO solution were found to form KOH·5DMSO and NaOH·4DMSO complexes that are stabilized due to the interligand interaction. Our present MP2/6‐311++G**//B3LYP/6‐31+G* computations show that 1 and 2 water molecules can build themselves into the MOH close surrounding without substantially perturbing the DMSO ligands and easily travel between different insertion positions. Our results predict that the activation energies in the series of reactions of nucleophilic addition to a triple bond with water, methanol, methanethiol, sodium hydrosulfide, and acetone in the presence of dihydrated complexes should be larger than those obtained with the participation of monohydrated ones, which is in fair agreement with the experimental findings. The present model also explains an increase in the ethynylation reaction yield in the presence of water by suppression of the competitive enolization reaction.

A CBS-Q//B3 based study has been carried out to elucidate the mechanism of the KOH/DMSO superbase catalyzed ketones nucleophilic addition to alkyl propargyl and alkyl allenyl ethers yielding, along with (Z)-monoadducts, up to 26% of unexpected (E)-diadducts. The impact of different substrates (alkynes versus allenes) on the reaction mechanism has been discussed in detail. Along with the model reaction of acetone addition to propyne and allene, the addition of acetone and acetophenone to methyl propargyl and methyl allenyl ethers is considered. The limiting reaction stage of the starting ketone carbanion addition to propargyl and allenyl systems occurs with activation energies typical for vinylation of ketones. In contrast, the addition of intermediate α-carbanions to the terminal position of methyl allenyl ether is associated with unusually low activation barriers. The results obtained explain the composition of the reaction products and indicate the participation of mainly the allene form in the reaction.

Base-Promoted Formationofa nA nnelated Pyrrolo-1,4-oxazine Ensemblefrom 1H-pyrrol-2-ylmethanol and Propargyl Chloride:ATheoretical and Experimental Study What prompted you to investigate this topic/problem?The Irkutsk School of Organic Chemistry has rich and broad experience in building and functionalizing pyrrole systems in ac onvenient and universal fashion. The work presented is ac ontinuation of as eries of investigations to activate several reactive centers of pyrrole with the aim to synthesize previously unknown compounds with promising properties, such as drugs and precursors of materials with specific characteristics.Invited for this month'sc over is the group of Prof. Dr.N adezhda M. Vitkovskaya at Irkutsk State University and the group of Dr.A ndrey V. Ivanova tt he A. E. Favorsky Irkutsk Institute of Chemistry,R ussian Federation.The image shows that three different pyrrole derivatives can be obtained from the same starting reagents. The reaction is easily controlled by the ratio of the reagents, the amount of alkali, and the degree of dilution.T he three strings of the balalaika (a Russianf olk instrument) that represent these parametersc an produce melodies from the same notes symbolizing the reagents. The sheets with quantum-chemical calculations under the musical notebooks ymbolize thatt he experimental work is based on the theoretical investigations. Read the full text of the article at

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The mechanism of aldol condensation of ketones in KOH/DMSO superbasic media has been investigated using the B2PLYP­(D2)/6-311+G**//B3LYP/6-31+G* quantum-chemical approach. It is found that the interaction of three ketone molecules resulting in the formation of the cyclohex-2-enone structure [isophorone or 3,5-dicyclohexyl-5-methylspiro(5.5)­undec-2-en-1-one] is thermodynamically more favorable than the interaction of two, three, or four molecules of ketone, resulting in the formation of linear products of the condensation. The formation of the condensation products with the isophorone skeleton can significantly hinder the cascade reactions of ketones with acetylenes [to afford 6,8-dioxabicyclo(3.2.1)­octanes or acylcyclopentenols] promoted by superbases. In particular, the kinetically more preferable reactions of autovinylation of 2-methyl-3-butyn-2-ol and autocondensation of acetone are the reasons why interaction of acetone with acetylene does not lead to the products of the cascade assemblies. The predominant formation of the products of these side reactions is confirmed experimentally.

The chemo-, regio- and stereoselective synthesis of pyrrole-fused pyrazine nitrones via the direct reaction of 2-carbonyl-N-allenylpyrroles (readily accessible from the corresponding NH-pyrroles) with hydroxyl amine hydrochloride has been developed. This...

Pyrrole synthesis from ketoximes and acetylene in the KOH/dimethyl sulfoxide (DMSO) superbase medium (here abbreviated as the KOA reaction) provided access to a wide variety of 2-substituted and 2,3-disubstituted pyrroles from the available starting materials (enolizable ketones and acetylene). All steps of the KOA reaction mechanism are studied, for the first time, in detail at a uniform theoretical level for the cascade assembly of 4,5,6,7-tetrahydroindole from cyclohexanone oxime and acetylene. Our results explain the reasons why some earlier postulated intermediates have not been detected during the reaction. Alternative channels for the formation of intermediates of 3H-pyrroles are considered. The qualitative agreement of the obtained results with kinetic studies is demonstrated.