Handbook of Functionalized Organometallics Applications in S

4.3 Further Applications of Functionalized Grignard Reagents
for the synthesis of a range of functionalized diarylamines such as 299a±c with
high yields (Scheme 4.65) [158].
EtO 2C
FG 2
H
N
I
(2.3 equiv)
OMe
1) iPrMgCl
-20 ºC, 0.5 h
NC
O 2N
H
N
FG 1
299a: 85% 299b: 78%
2)
-20 ºC, 2 h
3) FeCl 2/NaBH 4,rt,2h
Scheme 4.65 Polyfunctional diarylamines 299 obtained by the
reaction of a functionalized arylmagnesium compound with a
nitroarene. The dotted lines indicate the newly formed C±N
bond.
Br
FG 2
H
N
H
N
up to 95%
299c: 88%
The Grignard reagent may bear electron-withdrawing groups or electron-donating
groups. This is also the case for nitroarene and even heterocyclic nitroarenes
can be used in this reaction. Interestingly, sensitive functions like an iodine, bromine
or triflate [158] group can be present in either reaction partner. This is difficult
to realize for transition-metal catalyzed amination procedures [159,160,161].
This method shows an excellent functional-group tolerance and is almost indifferent
to the electronic properties of the reaction partners. However one equivalent
of Grignard reagent is wasted in the first reduction step. This can be avoided
by using a nitrosoarene instead of a nitroarene as the electrophilic reagent. The
reaction of 4-dimethylaminonitrosobenzene (304) with PhMgCl (1.2 equiv) provides
the expected diarylhydroxylamine 305 that, after reductive treatment (FeCl 2/
NaBH 4), gives the diarylamine 299d in 73% isolated yield (Scheme 4.66) [162,163].
O
N
NMe 2
PhMgCl
(1.2 equiv)
THF, -20 ºC, 1 h
Ph OH
N
NMe 2
FeCl 2/NaBH 4
rt, 2 h
Ph
NH
NMe 2
304 305 299d: 73%
Scheme 4.66 Synthesis of diarylamines using nitrosoarenes and Grignard reagents.
The difficult access to nitrosoarenes and their tendency to dimerize makes
these reagents less attractive. The substitution of the nitroso group with a toluenesulfonamide
leads to aryl 4-tolylazo sulfones of type 306, which can be used as
FG 1
N
Ph
151