Iodine(III)-Mediated Ring Contraction of 1,2-Dihydronaphthalenes: Mechanistic Insight by Computational Investigations

Abstract

The metal‐free synthesis of the trans‐1,3‐disubstituted indanes through the ring contraction of 1,2‐dihydronaphtalenes, promoted by PhI(OH)Ts (HTIB or Koser's reagent), was computationally studied using Density Functional Theory (DFT) methods. DFT calculations suggest that the stereoselectivity of these reactions arises through the torsional effects during the electrophilic addition of the hypervalent iodine to the double bond of the 1,2‐dihydronaphthalene. Furthermore, the fundamental role played by the solvent (MeOH) during the nucleophilic addition step was analyzed by DFT methods on a mixed continuum‐microsolvation model system.

A DFT study on the formation of heterocycles via iodine(iii)-promoted ring expansion reactions

“…In a previous computational study, we applied a continuum-microsolvation approach to describe the reaction mechanism involved in the ring contraction of 1,2-dihydronaphthalenes mediated by an iodine( iii ) compound. 74 Since then new theoretical studies have used the same approach exposing the relevance of solvent reactivity in hypervalent iodine-based reactions. 46,52,56,57…”

“…In the present study, in analogy to the methanol cluster previously reported, 74 we used continuum-microsolvation models composed by three molecules of water or methanol in order to evaluate the solvent effect in the nucleophilic addition of methanol to intermediate carbenium ion 14 , which has been previously suggested to be involved in the ring expansion reaction of methylene benzoannulenes (Scheme 3). 49…”

“…In contrast to our previous study on the HTIB-promoted ring contraction of 1,2-dihydronaphthalenes, 74 here we were able to obtain the transition states associated to the nucleophilic addition of only one water (or methanol) molecule to carbenium ion 14 without the assistance of a water- (or methanol-) cluster (more details in ESI†). Our calculations revealed that the addition assisted by only one water molecule was more energy demanding ( ca.…”

“…Hydrolysis step will convert 17M to 17W , completing the mechanism for the methanol pathway already described by some of us in the iodine( iii )-mediated ring contraction of 1,2-dihydronaphthalenes. 74 The optimized geometries for the methanol-assisted process are presented in ESI†(Fig. S6).…”

Hypercoordinate iodine(III) promoted reactions and catalysis: an update on current mechanistic understanding

“…The RE and S N 2 pathways were also studied using microsolvation and cluster‐continuum solvation models where the solute–solvent interaction is better described compared to the PCM or the SMD solvent continuum models . The results showed that S N 2 mechanism is favored over RE route.…”