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WIREs Comput Mol Sci
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Characterization of pericyclic steps in the mechanisms of Gold(I) catalyzed rearrangement of alkynes

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Abstract Pericyclic reactions are frequently proposed as intermediate steps in diverse multistep Au(I)‐catalyzed transformations of unsaturated systems, an expanding class of atom‐economical reactions that proceed under mild conditions and generally lead to products that exhibit an extraordinary increase in molecular complexity. The feasibility of pericyclic steps occurring in the overall transformations is greater with highly functionalized polyunsaturated systems. Experimental and computational studies concur that Au(I) catalyst guides, if possible, the evolution of the reactant and/or intermediates through pericyclic processes if available to the particular substrate. In general, the activation energies are lower than those for the corresponding reactions in the absence of the coinage metal, in particular when Au(I) is bound to a carbon atom of the pericyclic array. © 2012 John Wiley & Sons, Ltd. This article is categorized under: Structure and Mechanism > Reaction Mechanisms and Catalysis

Golden Carousel25 describing the facile interconversion between propargylic esters, allenyl esters, and gold carbene/carbocation esters due to the action of the Au(I) catalyst. The calculated energy barriers are in all transformations lower than 15.4 kcal/mol (BP86/TZVP*/SDD). Depending on the pattern of unsaturated substituents, different pericyclic rearrangements can be encountered in multistage mechanisms (Au–L = Au–PH3).

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Mechanism proposed for the rearrangement of alkynyl amine‐N‐oxides in the presence of an Au(I) catalyst through a pericyclic hetero‐retro‐ene reaction and representation of the transition structures for this step with and without Au(I) (B3LYP D3/6‐31G*/LANL2DZ, [Au] = AuPH3). (Modified with permission from Ref 99. Copyright 2012, American Chemical Society.)

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(A) Key Nazarov and Nazarov‐like reactions and the associated energy barriers for this transformation into the corresponding products (not shown), calculated at the B3LYP/6‐31G*(or 6‐311G*; LANL2DZ or SDD for Au(I)) level. (B) Calculated potential energy profile for the rearrangement of a propargylic vinyl ester to a cyclopentadiene (MP2/6‐31+G(d,p)/SDD//B3LYP/6‐31G(d)/SDD) through a Nazarov reaction ([Au] = AuPMe3).94 (C) Mechanistic proposal for both the aura‐iso‐Nazarov and aura‐Nazarov manifolds in the formation of indenyl indoles starting from propargylic indoles (B3LYP/6‐31G(d)/LANL2DZ, AuL = AuPH3). [Modified with permission from Refs 97 (copyright 2010, John Wiley & Sons) and 98 (copyright 2008, American Chemical Society).]

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Electrocyclic ring opening of a 2H‐oxete to afford the corresponding divinyl ketone product in the presence and absence of Au(I) activating the heteroatom. Energies calculated at the B3LYP/6‐31G(d)/LANL2DZ level (Au–L = Au–PH3). (Modified with permission from Refs 32 and 74. Copyright 2009 and 2008, American Chemical Society.)

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Potential energy surface for the 4πe‐electrocyclic ring opening of trans‐3,4‐dimethylcyclobutene‐1‐carboxylic acid to (E,E)‐ and (Z,Z)‐hexa‐2,4‐diene‐3‐carboxylic acid in the presence of model Au(PH3)+ acting as a Lewis acid on the olefin or the carboxylic acid and the corresponding thermal process (M06/6‐311+G(d,p)/SDD//B3LYP/6‐31G(d)/SDD). (Modified with permission from Ref 69. Copyright 2012, American Chemical Society.)

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Reaction profile of [4+2] cycloaddition and electrocyclic reaction mechanistic proposal for the overall rearrangement of 2‐alkynyl‐1,5‐diketones to cyclopentenediones. The energies (B2PLYP/6‐311+G(d,p)/LANL2DZ//B3LYP/6‐31G(d)/LANL2DZ) are given in kcal/mol. (Modified from Ref 63. Copyright 2010, John Wiley & Sons.)

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Proposed mechanism for the 1,3‐dipolar cycloaddition of o‐alkynyl‐nitrobenzene with ethyl vinyl ether in the presence of an Au(I) catalyst.51 Transition structures computed (at the B3LYP/6‐31G(d) level [/LANL2DZ for the Au atom]) for a (3+2) cycloaddition of 9 and ethyl vinyl ether in the presence and absence of Au(I) (modeled by AuPH3+). Gibbs free energy barriers (kcal/mol) for each step and the values for the distances of the forming σ bonds (in Å) are also shown.

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Calculated transition state of competing [4+2] versus Nazarov reaction in a substrate containing acetoxyallene and diene substructures (B3LYP/6‐31G(d)/LANL2DZ, [Au] = Au(PMe2Ph)). [Modified with permission from Refs 62 (copyright 2009, American Chemical Society) and 63 (copyright 2010, John Wiley & Sons).]

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Reaction profile for both (4C+2C)‐ and (4C+3C)‐cycloaddition mechanistic proposals for the rearrangement of allene dienes (X = C, E = CO2Me).52,56 The energy barriers as a function of the catalyst employed for the calculations are listed in the table. The energies are given in kcal/mol (M06/6‐311++G(d,p)/LACV3P++**//M06/6‐31G(d,p)/LACPV**).

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Mechanistic proposal for the competing (4C+2C)‐ and (4C+3C)‐cycloaddition pathways in the evolution of allenyl dienes in the presence of an Au(I) catalyst ([Au] = Au–PH3, Au–Cl, Au–P(OMe3), Au–PMe3, AuPPh3, Au–P(OPh3), Au–(tBu)2(o‐biPh)). [Modified with permission from Refs 52 (copyright 2009, American Chemical Society) and 56 (copyright 2011, Royal Society of Chemistry).]

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Relative energies of the calculated (B3LYP/6‐31G*/SDD level)41 Claisen‐like [3,3]‐sigmatropic rearrangement of the Au(I) complex 2. The energies are given in kcal/mol and the values between parentheses are the energy barriers for each TS ([Au] = Au–PH3).

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