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