Abstract
The detailed mechanism of the AuCN-catalyzed annulation of salicylaldehyde (SA) and phenyl acetylene leading to isoflavanone-type complexes has been investigated via density functional theory (DFT) calculations. Reaction pathways and possible stationary points are obtained with the combined molecular dynamics and coordinate driving (MD/CD) method. Our calculations reveal that the cyanide ion promoted umpolung hydroacylation/intramolecular oxa-Michael addition mechanism is more favorable than the Au(I)/Au(III) redox mechanism proposed previously. In the umpolung mechanism, the hydroxyl of SA is found to strongly stabilize the cyanide ion involved intermediates and transition states via hydrogen bond interactions, while the Au(I) ion always acts as a counter cation. The overall reaction is exergonic by 41.8 kcal/mol. The hydroacylation of phenyl acetylene is the rate-determining step and responsible for the regioselectivity with a free energy barrier of 27.3 kcal/mol. These calculated results are in qualitative accord with the experimental findings.
Highlights
The catalytic annulation of chelating aldehydes and unsaturated hydrocarbons provides a general, highly efficient, and atom-economical strategy to synthesize complex carbocyclic and heterocyclic frameworks (Willis, 2010)
We have performed density functional theory (DFT) calculations assisted by the molecular dynamics and coordinate driving (MD/CD) method to explore the detailed mechanism of the AuCNcatalyzed annulation of salicylaldehyde (SA) and phenyl acetylene
Our calculations reveal that a cyanide ion promoted umpolung hydroacylation/intramolecular oxa-Michael addition mechanism is more favorable than the Au(I)/Au(III) redox mechanism proposed previously
Summary
The catalytic annulation of chelating aldehydes and unsaturated hydrocarbons provides a general, highly efficient, and atom-economical strategy to synthesize complex carbocyclic and heterocyclic frameworks (Willis, 2010). The direct oxidative addition of the formyl Csp2-H bond of SA toward the Au(I) center via transition state TS5/Ia to form the Au(III) intermediate Ia is required to overcome a high activation barrier of 44.4 kcal/mol (relative to reactants), which is inconsistent with the experimental conditions that the reaction occurs at 150◦C.
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