Pd-catalyzed amination of a B-iodocarborane with various amine nucleophiles [251].
Smith and Maleczka have developed a one-pot synthesis of arylamine boronate esters
via sequential C–H borylation followed by Pd-catalyzed N-arylation (Eq. 46) [252].
The preparation of
18
F-labeled-N-arylindoles was accomplished through coupling
reactions of p18
F-C 6 H 4 I (Eq. 47) [253]. Importantly, these transformations were
effected in only 20 min, as the half-life of
18
F is short. Near stoichiometric quantities
of palladium were employed, but the reactions were conducted on extremely small
scale (7 mg of substrate), and the use of high catalyst loadings may have been due to
convenience rather than necessity. Pd-catalyzed sp
2 C–N bond forming reactions
involving halogenated naphthoquinones [254], ketal-protected piperidones [255],
sulfamides [256, 257], and N,N-dialkylhydrazines [258] have also been described.
Cl
O
N H
N
BPin
O
HBPin
(Ind)Ir(COD) (2 mol %)
dpme (2 mol %)
150 °C
Pd 2 (dba) 3 (1 mol %)
P(tBu) 3 (3 mol %)
K 3 PO 4 , DME
100 °C
73%
ð46Þ
N
H
N
N
Ph
Pd 2 (dba) 3
Davephos
NaOtBu, Toluene
100 °C, 20 min
84%
N
N
N
Ph
I
18 F
+
18 F
ð47Þ
4 Applications
4.1 Synthesis of Heterocycles via Reaction Sequences Involving
N-Arylation
Palladium catalyzed N-arylation reactions have been employed in a number of ringforming reactions that generate heterocyclic products [259–262]. In one of the
earliest publications on tin-free Pd-catalyzed N-arylation reactions, a number
indolines, tetrahydroquinolines, and benzoazepines were prepared via intramolecular N-arylation [263]. This strategy has subsequently been used for the generation of
several other clases of nitrogen heterocycles [264–271], including benzocazocenes
(e.g., 27) [272] and benzimidazo[1,2-a]quinolines (e.g., 28) [273] (Fig. 7).
The use of 1,2-dihaloarenes has been a key component of several recent annulation
reactions that afford nitrogen heterocycles [274–276]. For example, indoles were
prepared via a tandem amination/Heck reaction sequence between allylic amines
and o-bromoiodobenzene derivatives (Eq. 48) [277]. A synthesis of heterocycles
bearing three or more nitrogen atoms has been developed that proceeds via intermolecular N-arylation of a 3-aminopyridazine followed by intramolecular N-arylation of
the resulting product (Eq. 49) [278]. This latter strategy has also been applied to the
construction of other nitrogen-containing heterocycles [279].
24
G.S. Lemen and J.P. Wolfe
Smith and Maleczka have developed a one-pot synthesis of arylamine boronate esters
via sequential C–H borylation followed by Pd-catalyzed N-arylation (Eq. 46) [252].
The preparation of
18
F-labeled-N-arylindoles was accomplished through coupling
reactions of p18
F-C 6 H 4 I (Eq. 47) [253]. Importantly, these transformations were
effected in only 20 min, as the half-life of
18
F is short. Near stoichiometric quantities
of palladium were employed, but the reactions were conducted on extremely small
scale (7 mg of substrate), and the use of high catalyst loadings may have been due to
convenience rather than necessity. Pd-catalyzed sp
2 C–N bond forming reactions
involving halogenated naphthoquinones [254], ketal-protected piperidones [255],
sulfamides [256, 257], and N,N-dialkylhydrazines [258] have also been described.
Cl
O
N H
N
BPin
O
HBPin
(Ind)Ir(COD) (2 mol %)
dpme (2 mol %)
150 °C
Pd 2 (dba) 3 (1 mol %)
P(tBu) 3 (3 mol %)
K 3 PO 4 , DME
100 °C
73%
ð46Þ
N
H
N
N
Ph
Pd 2 (dba) 3
Davephos
NaOtBu, Toluene
100 °C, 20 min
84%
N
N
N
Ph
I
18 F
+
18 F
ð47Þ
4 Applications
4.1 Synthesis of Heterocycles via Reaction Sequences Involving
N-Arylation
Palladium catalyzed N-arylation reactions have been employed in a number of ringforming reactions that generate heterocyclic products [259–262]. In one of the
earliest publications on tin-free Pd-catalyzed N-arylation reactions, a number
indolines, tetrahydroquinolines, and benzoazepines were prepared via intramolecular N-arylation [263]. This strategy has subsequently been used for the generation of
several other clases of nitrogen heterocycles [264–271], including benzocazocenes
(e.g., 27) [272] and benzimidazo[1,2-a]quinolines (e.g., 28) [273] (Fig. 7).
The use of 1,2-dihaloarenes has been a key component of several recent annulation
reactions that afford nitrogen heterocycles [274–276]. For example, indoles were
prepared via a tandem amination/Heck reaction sequence between allylic amines
and o-bromoiodobenzene derivatives (Eq. 48) [277]. A synthesis of heterocycles
bearing three or more nitrogen atoms has been developed that proceeds via intermolecular N-arylation of a 3-aminopyridazine followed by intramolecular N-arylation of
the resulting product (Eq. 49) [278]. This latter strategy has also been applied to the
construction of other nitrogen-containing heterocycles [279].
24
G.S. Lemen and J.P. Wolfe