Gas-Phase Smiles Rearrangement of ortho-Nitro-substituted Diaryliodonium Cations and Their Mechanistic Insights
Wu-Zhi Wei1, 2, Cheng Pan3, Ling Lin2, Jianwei Han3,*, Hao-Yang Wang2,*
1School of Materials and Chemistry, University of Shanghai for Science and Technology, Shanghai, People’s Republic of China
2Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, People’s Republic of China
3Key Laboratory for Advanced Materials and Feringa Nobel Prize Scientist Joint Research Center, Department of Fine Chemistry and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai, People’s Republic of China
Correspondence:
Jianwei Han, Key Laboratory for Advanced Materials and Feringa Nobel Prize Scientist Joint Research Center, Department of Fine Chemistry and Institute of Fine Chemicals, School of Chemistry and Molecular Engineering, East China University of Science and Technology, Shanghai, 200237, People’s Republic of China. Email: jianweihan@ecust.edu.cn
Hao-Yang Wang, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai, 200032, People’s Republic of China. Email: haoyangwang@sioc.ac.cn
Rationale : Diaryliodonium salts are useful electrophilic reagents in organic chemistry, finding extensive applications in arylations and photo-induced polymerizations. However, the comprehensive mechanistic investigations, particularly concerning the mass spectrometric behaviors of diaryliodonium salts, are relatively scarce in the literatures.
Methods : Diaryliodonium salts could be readily ionized in ESI-MS to give [Ar1-I+-Ar2], and the high-resolution ESI-MS/MS experiments were conducted to investigate their gas-phase chemical reactions.
Results : Investigations on ESI-MS/MS of [Ar1-I+-Ar2] revealed two major fragmentation patterns: 1) Reductive elimination resulting the diaryl coupling product ion [Ar1-Ar2]+• by the loss of I. 2) Generating aryl cations [Ar1]+ or [Ar2]+ through cleavage of the C–I bonds. We unrevealed that the introduction of NO2into Ar2 of [Ar1-I+-Ar2] could lead to an unexpected fragmentation ion [Ar1O]+ in MS/MS, arising from an O-atom transfer process from NO2 to Ar1. Particularly, when NO2 wasortho -positioned to the iodine in Ar2, the [Ar1O]+ sometimes exhibited dominant behavior.
Conclusions : Comprehensive ESI-MS/MS studies and theoretical calculations provided strong support for the O-atom transfer mechanistic pathway: [Ar1-I+-(o -NO2-Ar2)] initially underwent a Smiles rearrangement to the intermediate [Ar1-O-(o -NO-Ar2I)]+, which subsequently dissociated to [Ar1O]+ or [o -NO-Ar2I]+•. Herein, we proposed an unexpected ”ortho -effect” in the gas-phase fragmentation reaction of [Ar1-I+-(o -NO2-Ar2)], in which the crucial determinant factor for the aryl migration was identified as the Smiles rearrangement reaction.
Key Words: Smiles Rearrangement, Nitro-substituted Diaryliodonium salts, ESI-MS/MS, O-atom transfer reaction