Chemistry Reference
In-Depth Information
Ph
RENORPHOS
108
Pd
2
(dba)
2
-CHCl
3
PPh
2
PhCO
2
H
Ph
Nf
NHNf
106
PPh
2
RENORPHOS
108
Benzene/hexane
107
(93%, 91% ee)
Scheme 5.34.
presence of Pd
2
(dba)
3
· CHCl
3
, PhCOOH, and (
R
,
R
) - renorphos
108
. Cyclization of alkyne
106
gave pyrrolidine
107
in 93% yield and 91% ee. The use of nonafl uorobutanesulfonyl
(Nf) group, instead of trifl uoromethanesulfonyl (Tf) group, gave the best result. Palla-
dium-catalyzed hydroamination would proceed through the formation of
π
- allylpalladium
intermediates.
Gold-catalyzed transformations have seen a fascinating development in catalysis in
recent years. Toste and others reported the enantioselective hydroamination of
N
-
allenyl sulfonamides catalyzed by (
R
) - xylyl - BINAP(AuOPNB)
2
[OPNB =
p
- nitroben-
zoate] (Scheme 5.35) [43a]. Gold(I)-catalyzed cyclization of allene
109
gave pyrrolidine
110
in 98% yield and 99% ee.
T
N
NHTs
Me
(
R
)-xylyl-BINAP(AuOPNB)
2
Me
CH
2
ClCH
2
Cl
Me
Me
109
110
(98%, 99% ee)
Scheme 5.35.
NHCbz
Cbz
N
Catalyst
115
AgClO
4
m
-Xylene
Et
Ph
Ph
MeO
MeO
PAr
2
AuCl
R
Ph
Ph
113
(83%, 91% ee from
111
)
PAr
2
AuCl
Et
Et
111
: R = Et
112
: R = Me
t
-Bu
Cbz
N
Cbz
N
Catalyst
115
Ar =
OMe
AgClO
4
m
-Xylene
+
Me
Et
Ph
Ph
Ph
Ph
t
-Bu
Et
Me
94% from
112
Catalyst
115
(
Z
)-
114
(96% ee)
(
E
)-
114
(76% ee)
Scheme 5.36.
Widenhoefer and others reported the gold(I)-catalyzed enantioselective hydroamina-
tion of
N
- allenyl carbamate
111
(Scheme 5.36) [43b]. Hydramination of allene
111
cata-
lyzed by a 1:2 mixture of the bis(gold) phosphine complex
115
and AgClO
4
forms the
corresponding pyrrolidine
113
with 91% ee. This catalytic hydroamination was extended
