Chemistry Reference
In-Depth Information
N
PhNHNH
2
Me
Ph
H
L10
2.5 mol% [Pd(cinnamyl)Cl]
2
,
, NaO
t
Bu
Me
> 95% yield (GC)
P(1-Ad)
2
Me
Cl
N
NH
2
Me
N
Me
Me
O
L10
PhNHNH
2
+
N
2
H
4
·H
2
O
L10
2.5 mol% [Pd(cinnamyl)Cl]
2
,
, NaO
t
Bu
>95% yield (GC)
no ArNHNHPh observed
Figure 5.10 Competition experiments involving the [Pd(cinnamyl)Cl]
2
/L10 catalyst
system, demonstrating high selectivity for the monoarylation of hydra-
zine over phenylhydrazine.
R
N
NH
2
R
[Pd(cinnamyl)Cl]
2
(2.5 mol%)
L1
R'
(2.5 mol%)
KO
t
Bu (2.5 equiv)
1,4-dioxane, 90 °C
N
-aminoindole
.
(2 equiv)
+
N
2
H
4
H
2
O
+
R
Br
N
H
R =
R =
(R' = Me)
OMe
(R' = H)
indazole
OMe
56%* (31%)
36%* (36%)
61%* (17%)
P(
t
Bu)
2
S
*yield of
N
-aminoindole
(yield of indazole)
PCy
2
Fe
L1
56%* (34%)
65%* (23%)
Figure 5.11 Tandem palladium-catalyzed cross-coupling-hydroamination reactions
of hydrazine with 2-alkynylbromoarenes to afford N-aminoindole/inda-
zole products.
catalyst system exhibits a clear preference for hydrazine over arylhydrazine as
a substrate in BHA, leading to selective hydrazine monoarylation.
57
The successful application of [Pd(cinnamyl)Cl]
2
/L1 catalyst mixtures in the
BHA of hydrazine with 2-alkynylbromoarenes to afford N-aminoindoles and
indazoles was reported by Stradiotto and co-workers (Figure 5.11).
35
Al-
though in all cases the N-aminoindole product was favored, the formation of
appreciable quantities of the analogous indazole serves to limit the synthetic
utility of this protocol; efforts to achieve greater selectivity by altering the
base or solvent or by including additives (e.g., CuCl
2
or Ag
2
CO
3
) were un-
successful. It is interesting that despite the ecacy of palladium catalysts
featuring L10 in the selective monoarylation of hydrazine (Figure 5.9),
57
[Pd(cinnamyl)Cl]
2
/L10 catalyst mixtures performed poorly in comparison
with L1-based palladium catalysts in these tandem BHA-hydroamination
processes.
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