Gas‐phase Smiles rearrangement of ortho‐nitro‐substituted diaryliodonium cations and their mechanistic insights

Abstract

RationaleDiaryliodonium salts are useful electrophilic reagents in organic chemistry, finding extensive applications in arylations and photo‐induced polymerizations. However, comprehensive mechanistic investigations, particularly concerning the mass spectrometric behaviors of diaryliodonium salts, are relatively scarce in the literature.MethodsDiaryliodonium salts could be readily ionized using electrospray ionization mass spectrometry (ESI‐MS) to give [Ar1‐I+‐Ar2], and high‐resolution ESI‐tandem mass spectrometry (MS/MS) experiments were conducted to investigate their gas‐phase chemical reactions.ResultsInvestigations on ESI‐MS/MS of [Ar1‐I+‐Ar2] revealed two major fragmentation patterns: (1) reductive elimination resulting in the diaryl coupling product ion [Ar1‐Ar2]+• by the loss of I; (2) generation of aryl cations [Ar1]+ or [Ar2]+ through cleavage of the C–I bonds. We revealed that the introduction of NO2 into 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 was ortho‐positioned to the iodine in Ar2, the [Ar1O]+ sometimes exhibited dominant behavior.ConclusionsComprehensive 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.