Asymmetric Total Syntheses of Kopsane Alkaloids via a PtCl2 -Catalyzed Intramolecular [3+2] Cycloaddition

A concise and asymmetric total synthesis of five kopsane alkaloids that share a unique heptacyclic caged ring system was accomplished. The key transformation in the sequence involved a remarkable PtCl₂ -catalyzed intramolecular [3+2] cycloaddition, which allowed for the rapid assembly of pentacyclic carbon skeletons bearing 2,3-quaternary functionalized indoline. Expeditious construction of diverse indoline scaffolds with excellent control of diastereoselectivity demonstrated the broad scope and versatility of this key transformation.

Unveiling the mechanisms and secrets of chemoselectivities in Au(i)-catalyzed diazo-based couplings with aryl unsaturated aliphatic alcohols

The mechanisms and origins of the unsaturated-aliphatic-alcohols-modulated chemoselectivity of Au-catalyzed carbene transfers from diazo compounds are disclosed by DFT studies.

DFT study on the reaction mechanisms and stereoselectivities of NHC-catalyzed [2 + 2] cycloaddition between arylalkylketenes and electron-deficient benzaldehydes

In this paper, two possible mechanisms (mechanisms A and B) on the stereoselective [2 + 2] cycloaddition of aryl(alkyl)ketenes and electron-deficient benzaldehydes catalyzed by N-heterocyclic carbenes (NHCs) have been investigated using density functional theory (DFT). Our calculated results indicate that the favorable mechanism (mechanism A) includes three processes: the first step is the nucleophilic attack on the arylalkylketene by the NHC catalyst to form an intermediate, the second step is the [2 + 2] cycloaddition of the intermediate and benzaldehyde for the formation of a β-lactone, and the last step is the dissociation of the NHC catalyst and the β-lactone. Notably, the [2 + 2] cycloaddition, in which two chiral centers associated with four configurations (SS, RR, SR and RS) are formed, is demonstrated to be both the rate- and stereoselectivity-determining step. Moreover, the reaction pathway associated with the SR configuration is the most favorable pathway and leads to the main product, which is in good agreement with the experimental results. Furthermore, the analysis of global and local reactivity indexes has been performed to explain the role of the NHC catalyst in the [2 + 2] cycloaddition reaction. Therefore, this study will be of great use for the rational design of more efficient catalysts for this kind of cycloaddition.

Mechanistic insight into water-modulated cycloisomerization of enynyl esters using an Au(i) catalyst

The Au(i)-catalyzed cycloisomerization reactions of 1,6-enylnyl ester are theoretically investigated to rationalize the observed product divergences by modulating H₂O participation.

Mechanism of AuCl₃-catalyzed cyclization of 1-(indol-2-yl)-3-alkyn-1-ols: a DFT study

A computational study with the B3LYP functional was carried out to elucidate the mechanisms of AuCl₃- and AgOTf-catalyzed cyclization of 1-(indol-2-yl)-3-alkyn-1-ols. The theoretical studies suggested that the two main processes, cycloaddition and hydrogen-transfer, are included in all possible reaction pathways. Calculations revealed that AuCl₃ is more effective in catalytic ability than AgOTf to catalyze the cyclization of 1-(indol-2-yl)-3-alkyn-1-ols into carbazole derivatives. More importantly, we found that the ligands of catalysts, Cl⁻ and OTf⁻, are critical in a stepwise proton-transport process involved in intramolecular nucleophilic addition because they act as a proton shuttle to lower the activation free energy barrier of the rate-determining step. The theoretical discovery of the role of ligands of catalysts in hydrogen shift process suggests that AuCl₃- and AgOTf-catalyzed cyclization of 1-(indol-2-yl)-3-alkyn-1-ols can be accelerated when ligands with the property of nucleophile are used. Our theoretical calculations reproduced the experimental results very well. The present study is expected to help understand other transition metal-catalyzed reactions and to give guidance for future design of new catalysts.