Figure 4 High-resolution ESI-MS/MS of
[M –OTf]+: (a ) 13 ,
(b ) 14 , (c ) 15 and (d )16 .
However, the formation of product ions
[Ar1O]+ from
[Ar1-I+-(o -NO2- Ar2)]
cations could not be simply rationalized by a one-step bond cleavage
process. All the experimental results suggested that in the case of
[Ar1-I+-(o -NO2-Ar2)],
a Smiles rearrangement initially occurred, with the O-atom from the
nitro group attacking the C(ipso) position of
Ar1I via a six-membered ring transition state, leading
to the formation of the intermediate
[Ar1-O-(o -NO-Ar2I)]+.
This transformation was accompanied by the reduction of the iodine (III)
species to the corresponding iodine (I) species, which ultimately
dissociated to produce [Ar1O]+(such as [MesO]+ at m /z 135 in MS/MS
of [5 –OTf]+, as shown in Scheme
4 and Figure 2a ). This dissociation was achieved through the
loss of neutral [o -NO-Ar2I] or the
generation of
[o -NO-Ar2I]+• by the loss
of Ar1O•. The ESI-MS/MS of
[M –OTf]+ (M =13 ~22 shown in Figure
4a~d and S13 ~S22 )
exhibited striking similarity to the MS/MS of
[5 –OTf]+, all prominently featuring
[MesO]+ at m/z 135 as the dominant fragment
ion. Therefore, this unexpected ”ortho effect” observed in the
gas-phase fragmentation reaction of
[Ar1-I+-(o -NO2-Ar2)]
cations could likely be attributed to the Smiles rearrangement induced
by the ortho effect of the nitro group.