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O
B
2
Pin
2
CuCl, Walphos
(97)
NaO
t
Bu, MeOH
O
BF
3
K
B(dan)
O
A
r
ArBr
Pd(OAc)
2
, XPhos
K
2
CO
3
Toluene/water
80 °C
MeO
B(dan)
MeO
MeO
B(dan)
96
95
98, >99% e.s.
1. ester to amide
2. B(dan) to BF
3
K
F
3
C
CF
3
PPh
2
CF
3
P
CH
3
Ar'Br
O
A
r
O
Ar
Fe
P
d(OAc)
2
, XPhos
K
2
CO
3
CPME/H
2
O
80 °C
N
BF
3
K
N
Ar'
CF
3
97
99
100, >99% e.s.
Scheme 11.11 Hall method for the sequential coupling of b-diboryl carbonyl
compounds.
(11
:
23)
101
102
enriched boronic esters 104 [eqn (11.24)].
32
This provides a very significant
advance in the synthesis of chiral organoboron compounds.
Bpin
Ar-I
Ar
Bpin
R
Pd(OAc)
2
Bpin
R
103
104
KOH,
H
2
O/dioxane
typically 90% ee
(11
:
24)
Ar
Ar
O
O
Me
P
NMe
2
Me
O
O
Ar
Ar
Hence although the enantiospecific cross-coupling of secondary boronic
esters is still limited in scope, there have been significant advances in the
past few years such that this reaction is now feasible with a variety of sub-
strates, expanding the utility of this reaction past the initially discovered
cyclopropyl systems. Importantly, these advances are starting to find prac-
tical applications in complex synthesis. For example, the silver-mediated
cross-coupling of benzylic boronic esters under Crudden conditions has
been used by Li and Burke to effect the critical, stereoretentive coupling step
in the total synthesis of the 1,1-diarylethane 48, which is a glucagon receptor
antagonist being examined for treatment of type II diabetes [eqn 11.15)].
53
Clearly, these new advances in the Suzuki-Miyaura reaction are already
providing facile access to compounds that are dicult to prepare by other
routes. Further developments in this area will only increase the scope and
potential applications of this already powerful reaction.
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