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The mechanism, stereoselectivity, and regioselectivity in the Au- and Pt-catalyzed cycloadditions of indolyl-allenes were explored by density functional theory (DFT). Three different catalytic syst...

This study is devoted to a theoretical investigation of the mechanism, regioselectivity, role of catalyst, and effect of substituent and solvent in the Au-catalyzed cascade reaction between 1,4-diynes and pyrroles. Density functional theory (DFT) calculations indicate that this reaction comprises four principal stages: (1) formation of different intermediates through the first intermolecular hydroarylation, (2) 1,3-H transfer to give the enyne intermediates, (3) a second intermolecular hydroarylation, and (4) a second proton transfer along with Au(I) catalyst regeneration and final product formation. In addition, the computational results suggest that the first regioselectivity is determined by the electronic effects of the reagents. However, the torsional strains within the transition structures (intramolecular cyclization) and electronic effects of enyne intermediates would account for the second regioselectivity. A global reactivity index (GRI) analysis for different gold catalysts (namely, IPrAu+, PPh...

The present study reports a detailed theoretical analysis of the mechanistic and chemoselectivity features in 1,6-diyne ester cycloisomerization. The energy profiles for three different catalysts, namely, [AuI(PPhMe2)(NCMe)]+, [AuIII(Cl)2(pic)] (pic = 2-picolinate), and PtCl2, were investigated. The DFT calculations reveal that all of these catalysts entail similar 1,3-acyloxy migration and 5-exo-dig cyclization steps, whereas completely distinct reaction pathways are observed after the formation of the putative vinyl metal complex intermediates. In the [AuI(PPhMe2)(NCMe)]+ system, the configuration of the phosphine ligand can explain the exclusive chemoselectivity of the Friedel–Crafts reaction over the 1,5-acyl migration. On the other hand, in the [AuIII(Cl)2(pic)] and PtCl2 systems, the 1,5-acyl migration is assisted by the chloride ligand, offering an alternative mechanism that can justify a reasonable activation barrier and the corresponding stereochemical feature in the reaction. Moreover, the [AuI(...

This study reports a detailed theoretical analysis of the mechanisms and chemoselectivity for the formation of benzo[b]fluorenes or benzofulvenes from propargyl esters catalyzed by an organometallic Au(I) complex. Three different substitution patterns within the 1,5-diyne ester substrates were explored to rationalize the reaction mechanism and chemoselectivity. DFT calculations reveal that the title reaction proceeds through four main steps: (i) 1,3-acyl-shift, (ii) 6-endo-dig or 5-exo-dig cyclization, (iii) Friedel–Crafts-type, and (iv) proton transfer, with step (ii) being rate-determining in all studied pathways. In the absence of substituents at the aromatic rings of the substrate (R = H), the 6-endo-dig cyclization is favored. In turn, in the presence of one strong electron-donating substituent at the backbone (R = OCH3) of the substrate, the 5-exo-dig cyclization is favored. Besides, a modification of the substrate’s acetyl group by a pivaloyl group leads to an activation barrier difference between ...

We report here the theoretical analysis of the mechanism and regioselectivity of the direct insertion of silane moieties into the C–N bond of N-heterocyclic carbenes leading to eventual ring expans...

The mechanisms of PtCl2-catalyzed rearrangement of cyclopropenes to allenes have been investigated using density functional theory calculations carried out at the B3LYP/6-31G(d,p) (LANL2TZ(f) for P...

The mechanisms of the gold(I)-catalyzed rearrangement of homopropargyl sulfoxides have been investigated using density functional theory calculations done at the B3LYP/6-31G(d, p) (SDD for Au) level of theory. Solvent effects on these reactions have been explored by calculations that included a polarizable continuum model (PCM) for the solvent (CH2Cl2). Two plausible pathways which lead to the formation of benzothiepinones or benzothiopines via an α-carbonyl Au carbenoid through 5-exo-dig cyclization or 6-endo-dig cyclization were proposed. Our calculation results suggested the following. (1) The first step of the cycle is nucleophilic addition of the sulfoxide oxygen onto the triple bond to form an alkenyl gold intermediate through 5-exo-dig cyclization or 6-endo-dig cyclization. The alkenyl gold species is then capable of pushing out the sulfide moiety, forming an α-carbonyl Au carbenoid. Finally, α-carbonyl Au carbenoids undergo intramolecular Friedel–Crafts alkylation to produce the observed products ...

The mechanism and regioselectivity of gold(I)-catalyzed synthesis of highly substituted furans based on 1-(1-alkynyl)cyclopropyl ketones with nucleophiles have been investigated using density funct...