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O
Ar B(OH)
2
Pd(MeCN)
2
(OTs)
2,
L, Cu(OTf)
2
O
2,
3Å MS, DMF, r.t., 24 h
O
OH
R
F
3
C
()
n
R'
R
()
n
N
N
Ar
R'
L
Scheme 9.144 Enantioselective oxidative arylation of unsaturated alcohols (only the
major product is shown).
Pd(OA c)
2
(5 mol% )
L (7.5 mol%)
Cu (OAc )
2,
THF, r.t.,12 h
B(O H)
2
+
Ph
O
O
L
(R)-BINAP
(R)-MeOBip hep
Yie ld, % (
ee
)
71 (57)
67 (82)
Scheme 9.145 Enantioselective deborylative Heck reaction.
B(O H)
2
LPd(O Ac)
2
(5 mol %)
O
2,
DMF, r.t.,16 h
+
CHO
CHO
Ph
74% (
ee
75%)
Scheme 9.146 Enantioselective deborylative arylation of an enal.
The hypothesis that oxidative Heck reactions involving deborylation must
proceed via the polar pathway prompted Gelman and co-workers
405
to in-
vestigate the application of this reaction in enantioselective mode using
chiral ligands normally used with success in the enantioselective Mizoroki-
Heck reaction, including BINAP and oxazoline chelators.
120
The results were,
however, inferior with respect to both material and optical yields and some
ligands highly effective in enantioselective Mizoroki-Heck reactions failed in
the deborylative version (Scheme 9.145). However, the new reaction took
place under substantially milder conditions and was significantly faster,
which promises further improvements.
Similar results were obtained by Jung and co-workers using a different
system with N,N-chelators, O
2
as terminal oxidant and an open-chain al-
kene.
406
The optical yields obtained were fairly high (around 70%) provided
that a preformed complex was used as precatalyst to minimize the ligand-
unrestricted pathways (Scheme 9.146).
In this respect, a few comments are should be made. The use of bidentate
ligands is not a guarantee of the realization of the polar pathway. When
using Pd(OAc)
2
as a Pd source, the catalytic species would contain an OAc
ligand, which is a good ligand for palladium with a stable or hemi-labile
mode of binding, not easily displaced by olefin. Therefore, the reaction may
(or even must) take place via a neutral pathway with dechelation, leaving the
chiral
ligand in the transition state and intermediates bonded in a
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