Quantum-Chemical Study of the Assembly Mechanism of 1-Pyrrolines from -Benzylaldimines and Arylacetylenes in KOBu/DMSO Superbasic Medium.

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 -benzyl-1-phenylmethanimine and phenylacetylene in the superbasic medium KOBu/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.

Semistabilized Diazatrienyl Anions from Pyridine Imines and Acetylenes: An Access to ()-Stilbene/Imidazopyridine Ensembles, Benzyl Imidazopyridines, and Beyond.

Semistabilized diazatrienyl anions are generated by the reaction of 2-pyridylarylimines with arylacetylenes in superbase systems MOBu (M = Li, Na, K)/DMSO at ambient temperature for 15 min. The initial intermediate -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 ()-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*).

Aldol Condensation Superbase-Catalyzed Addition of Ketones to Acetylenes: A Quantum-Chemical and Experimental Study.

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.

Self-Assembly of -Phenyl-2,5-dimethylpyrrole from Acetylene and Aniline in KOH/DMSO and KOBu/DMSO Superbase Systems: A Quantum-Chemical Insight.

By employing the contemporary B2PLYP(D3)/6-311+G**//B3LYP/6-31+G* method of quantum chemistry, we unraveled the mechanism of a recently discovered cascade assembly of -phenyl-2,5-dimethylpyrrole from one molecule of aniline and three molecules of acetylene activated by KOH/DMSO and KOBu/DMSO superbase systems. For the established mechanism, we compare and analyze the activity of these two superbases. The reaction is found to be activated by the interaction of aniline with acetylene, and the barrier associated with this interaction turns out to be the limiting one.

Transition-Metal-Free C-Vinylation of Ketones with Acetylenes: A Quantum-Chemical Rationalization of Similarities and Differences in Catalysis by Superbases MOH/DMSO and tBuOM/DMSO (M = Na, K).

Transition-metal-free C-vinylation of acetone with phenylacetylene catalyzed by superbases MOH/DMSO and tBuOM/DMSO (M = Na, K) has been theoretically evaluated in the B3LYP/6-311++G**//B3LYP/6-31+G* approach to rationalize similarities and differences in activity of the above catalytic systems. The close solvate surroundings of sodium and potassium tert-butoxides have been studied. Formation of tBuOM· nDMSO complexes and their structure and thermodynamic stability are discussed in comparison with similar complexes of alkali-metal hydroxides MOH· nDMSO.

Nucleophilic Addition of Ketones To Acetylenes and Allenes: A Quantum-Chemical Insight.

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.