3.1.3 Other Nitrogen Compounds
Without doubt, amines and amides are the most common nitrogen coupling
components in palladium-catalyzed vinylation reactions. However, cross-couplings
of such type proved rather versatile and tolerant to the employment of other nitrogen
compounds too. In this respect, Barluenga introduced the readily available
N-trialkylsilyl imines as synthetic equivalents of the highly unstable NH-aldimines
and reported their efficient application in C–N bond forming processes (Scheme 16)
[71]. The use of Pd 2 (dba) 3 in combination with either BINAP or DavePhos assisted
the reaction of b-bromostyrene with silyl imines derived from benzaldehyde and
cinnamaldehyde to afford the corresponding 2-azadienes and 3-azatrienes, respectively, in high yields.
More recently, they have reported the coupling of vinyl halides with tert-butyl
carbazate to yield rather functionalized and unusual types of hydrazines (Scheme 17)
[72]. In this case, the success of the process relied on the use of the phosphine-type
ligand Johnphos in combination with Pd 2 (dba) 3 . Furthermore, the proper choice of
base played a determinant role in circumventing the formation of the Ullmann-type
homocoupling compound as a side product. Under the optimized conditions, a wide
range of vinyl halides (b-bromostyrene, 1-bromodienes, 4-bromoenynes, and even
less-reactive 1-chlorodienes) smoothly underwent the coupling process to furnish the
target N-alkenylhydrazines.
Bolm employed NH-sulfoximines as nitrogen nucleophiles in palladium-catalyzed
vinylations (Scheme 18) [73]. These kinds of derivatives are of utmost synthetic
N
TMS
R
n
Pd 2 (dba) 3 (2 mol%),
DavePhos (4 mol%)
NaO-tBu, toluene
90 ºC
90-93%
Ph
+ Br
N
R
n
Ph
n = 0,1
Scheme 16 Palladium-catalyzed vinylations of N-trialkylsilyl imines
Pd2(dba)3 (1-2 mol%),
JohnPhos (8 mol%)
Cs 2 CO 3 , DMF,
90-110 ºC
50-82%
R
+
X
NH
Boc
H 2 N
R
N
Boc
H 2 N
X = Br, Cl
Scheme 17 Palladium-catalyzed vinylations of tert-butylcarbazate
+
NH
S
R 1
R 2
O
R 3
B r
R 5
R 4
Pd(OAc) 2 (0.5-1 mol%),
rac-BINAP (0.75-1.5 mol%)
NaO-tBu, toluene,
110 ºC
up to 98%
N
S
R 1
R 2
O
R 3
R 4
R 5
Scheme 18 Palladium-catalyzed vinylations of NH-sulfoximines
66
A. Correa and C. Bolm
Without doubt, amines and amides are the most common nitrogen coupling
components in palladium-catalyzed vinylation reactions. However, cross-couplings
of such type proved rather versatile and tolerant to the employment of other nitrogen
compounds too. In this respect, Barluenga introduced the readily available
N-trialkylsilyl imines as synthetic equivalents of the highly unstable NH-aldimines
and reported their efficient application in C–N bond forming processes (Scheme 16)
[71]. The use of Pd 2 (dba) 3 in combination with either BINAP or DavePhos assisted
the reaction of b-bromostyrene with silyl imines derived from benzaldehyde and
cinnamaldehyde to afford the corresponding 2-azadienes and 3-azatrienes, respectively, in high yields.
More recently, they have reported the coupling of vinyl halides with tert-butyl
carbazate to yield rather functionalized and unusual types of hydrazines (Scheme 17)
[72]. In this case, the success of the process relied on the use of the phosphine-type
ligand Johnphos in combination with Pd 2 (dba) 3 . Furthermore, the proper choice of
base played a determinant role in circumventing the formation of the Ullmann-type
homocoupling compound as a side product. Under the optimized conditions, a wide
range of vinyl halides (b-bromostyrene, 1-bromodienes, 4-bromoenynes, and even
less-reactive 1-chlorodienes) smoothly underwent the coupling process to furnish the
target N-alkenylhydrazines.
Bolm employed NH-sulfoximines as nitrogen nucleophiles in palladium-catalyzed
vinylations (Scheme 18) [73]. These kinds of derivatives are of utmost synthetic
N
TMS
R
n
Pd 2 (dba) 3 (2 mol%),
DavePhos (4 mol%)
NaO-tBu, toluene
90 ºC
90-93%
Ph
+ Br
N
R
n
Ph
n = 0,1
Scheme 16 Palladium-catalyzed vinylations of N-trialkylsilyl imines
Pd2(dba)3 (1-2 mol%),
JohnPhos (8 mol%)
Cs 2 CO 3 , DMF,
90-110 ºC
50-82%
R
+
X
NH
Boc
H 2 N
R
N
Boc
H 2 N
X = Br, Cl
Scheme 17 Palladium-catalyzed vinylations of tert-butylcarbazate
+
NH
S
R 1
R 2
O
R 3
B r
R 5
R 4
Pd(OAc) 2 (0.5-1 mol%),
rac-BINAP (0.75-1.5 mol%)
NaO-tBu, toluene,
110 ºC
up to 98%
N
S
R 1
R 2
O
R 3
R 4
R 5
Scheme 18 Palladium-catalyzed vinylations of NH-sulfoximines
66
A. Correa and C. Bolm