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mild protocol using CaCO
3
as base and Pd(OAc)
2
or Pd/C in MeOH.
270
As
with other reactions involving diazonium salts, I and Br derivatives are not
reactive under the mild conditions employed, thus allowing the retention of
halogen atoms in the products (Scheme 9.79).
Arylation of bis-Boc-protected allylamine requires the use of Pd(0) pre-
catalyst and different conditions for electron-rich and electron-deficient
aryls using NaOAc or CaCO
3
bases (Scheme 9.80).
271
This protocol was used for the synthesis of indoles by consecutive Heck
reactions - intermolecular arylation of N,N-disubstituted allylamine fol-
lowed by intramolecular exo-trig cyclization. Worth of note is that the second
Heck reaction requires different catalytic system and re-charging of Pd
precatalyst (Scheme 9.81).
271
Whereas intramolecular Mizoroki-Heck reactions have been known for
decades and provide a well-established tool for the synthesis of various
heterocycles, such an approach with arenediazonium salts was unknown
N
2
BF
4
O
Pd(OAc)
2
(2 mol%)
CaCO
3,
MeOH, r.t.
+
80%
I
O
I
Scheme 9.79 Example of mild arylation of methyl vinyl ketone by arenediazonium
salts, showing retention of iodine substituent.
N
2
BF
4
Pd
2
(dba)
3
(4 mol%)
base, solvent, r.t., 1.5-6 h
N(Boc)
2
+
R
N(B oc)
2
R = H; o -, p-MeO; o-Ph ; 2,4- Me
2
;3,5-Me
2
base/solvent = NaOAc/MeCN
R=m-CF
3
;p-CN, Ac, CO
2
Me, Cl, Br , I; o-Cl, B r
base/solvent = CaCO
3
/MeOH
61-9 0%
R
Scheme 9.80 Arylation of protected allylamine.
Ph
PhN
2
BF
4
Pd
2
(dba)
3
NaOAc, MeCN
r.t., 1 h
I
I
N
COCF
3
N
COCF
3
Ph
Pd( OAc)
2,
(o-tol)
3
P
Et
3
N, 80°C , 12 h
N
COCF
3
50%
Scheme 9.81
Intramolecular arylation of allylamine, an example.
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