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O
O
TMS
TMS
O
D
D
TMS
TMS
O
O
5
6
a
e
b
2
9
22
D
D
c
d
CN
NC
MeO
2
C
CO
2
Me
NC
CN
Scheme 9 Reactivity of 22 [
51
]. Conditions: (
a
) using 2,3,8,9-tetrakis(trimethylsilyl)-22 as the
starting material, dimethyldioxirane (DMDO), acetone, 26%, (
b
) methylene blue (0.9 equiv.),
O
2
,CH
2
Cl
2
,h
, 78%, (
d
) DMAD (1.6 equiv.), AlCl
3
(0.1 equiv.), PhCH
3
, 74% (
e
) (1) CF
3
CO
2
D, CDCl
3
,60
C, 80% (2) CF
3
CO
2
D, CDCl
3
, 100
C,
82%
n
, 70%, (
c
) TCNE (1 equiv.), CH
3
CN,
D
phenylene (25)[
52
]. Epoxidation of the unsubstituted 22, however, only proceeded
twice, leaving the bay region double bond unreacted [
51
]. The diene composed
of the more reactive double bonds underwent [4
2] cycloadditions with either
singlet oxygen (
1
O
2
), tetracyanoethylene (TCNE), or DMAD, followed by a second
electrocyclic reaction to give the product shown (Scheme
9
b-d).
Lastly, the deuteration of 22 was attempted in order to examine more generally
its reactivity towards electrophiles. Biphenylene [
14
] and 25 [
53
] both undergo
deuteration exclusively at the
รพ
b
position (C2/9). However, for 22 deuteration occurs
a
b
preferentially at the
position under
harsher conditions (Scheme
9
e) [
51
]. Calculations (HF/6-31G*) of the protonated
intermediates indicated that attack at C5/6 results in the fewest resonance forms
with cyclobutadienoid character. Additionally, this reactivity trend corresponds to
the relative size of the HOMO coefficients (HF/STO-3G) at those positions.
position (C5/6) and then secondarily at the
2.4 Applications of Phenylene-Containing Materials
There is a fair amount of interest in the effect of incorporating antiaromatic
moieties into systems that normally rely on aromatics to perform a function. In
these cases, biphenylene is often turned to as a stable substitute for cyclobutadiene.
Previous work has clearly demonstrated that this scaffold is not purely
antiaromatic; however, the model systems have had some informative results.
In several cases,
-complexes of [N]phenylenes have been shown to undergo
intramolecular inter-ring haptotropic rearrangements (IRHR). Depending on the
p
