Search for: All records

Computations were used to model the rearrangement of the barbaralyl cation, a structure that demonstrates nonclassical bridging, homoconjugation, fluxionality, non-statistical dynamic effects, post-transition state bifurcations, and tunneling! 

Abstract Recently, Huang and co‐workers reported a catalytic reaction that utilizes H₂as the sole reductant for a C−C coupling of allyl groups with yields up to 96 %. Here we use computational quantum chemistry to identify several key features of this reaction that provide clarity on how it proceeds. We propose the involvement of a Pd−Pd bound dimer precatalyst, demonstrate the importance of ligand π‐π interactions and counterions, and identify a new, energetically viable, mechanism involving two dimerized, outer‐sphere reductive elimination transition structures that determine both the rate and selectivity. Although we rule out the previously proposed transmetalation step on energetic grounds, we show it to have an unusual aromatic transition structure in which two Pd atoms support rearranging electrons. The prevalence of potential metal‐supported pericyclic reactions in this system suggests that one should consider such processes regularly, but the results of our calculations also indicate that one should do so with caution. 

Abstract Stereoselective Zweifel olefination using boronate complexes carrying two different reactive π‐systems was achieved to synthesize vinyl heteroarenes and conjugated 1,3‐dienes in good yield and up to 100 % stereoselectivity, which remains unexplored until now. Most importantly, we report the unprecedented formation ofEvs.Z‐vinyl heteroarenes for different heteroarenes under identical conditions. Density functional theory (DFT) investigations unveil the mechanistic dichotomy between olefin and heteroarene activation followed by 1,2‐migration, leading toEorZ‐vinyl heteroarenes respectively. We also report a previously unknown reversal of stereoselectivity by using 2,3‐Dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) as an electrophile. The Zweifel olefination using a boronate complex that carries two different olefins was previously unexplored due to significant challenges associated with the site‐selective activation of olefins. We have solved this problem and reported the site‐selective activation of olefins for the stereoselective synthesis of 1,3‐dienes. 

Abstract Density functional theory was used to elucidate the mechanism and the pericyclicity of chromium‐catalyzed bicyclization reactions that purportedly involve 8‐electron electrocyclization steps. Our computational results indicate that these reactions do indeed proceed via 8‐electron electrocyclization rather than an alternative pathway involving 4‐electron electrocyclization followed by Cope rearrangement. The role of C=[M] groups on the electrocyclization, specifically its pericyclicity, was examined in detail using modern theoretical tools.