Chemistry Reference
In-Depth Information
Table 12.3
Continued
)
O
O
1 mol% Cu precursor, 4 mol% ligand*
+ 1.4 equiv AlMe
3
*
Et
2
OorTHF
C
5
H
11
C
5
H
11
Conversion
(%)
b
1,4-Selectivity
c
Yield
d
(%)
Entry
Ligand
Precursor
ee (%)
e
Reference
O
O
O
O
O
O
P
O
O
69f
(R)
ax
R
3
6
Cu(OTf)
2
91
Nd
66
52
(R)
[33]
=
H
a) Typical reaction conditions: Cu precursor (1 mol.%), ligand (4 mol.%), AlMe
3
(1.4 equiv ), and substrate (1 equiv) unless
otherwise stated.
b) % Conversion determined by GC using undecane as internal standard.
c) Regioselectivity determined by GC using undecane as internal standard.
d) Yield determined by CG using undecane as internal standard, otherwise not determined (Nd).
e) Enantiomeric excess determined by GC.
f) Ligand-to-Cu ratio
=
2.
enantioselectivities (90%, 80% ee, Table 12.4, entry 3) were obtained with ligand
50f,
which contains sterically encumbered biaryl phosphite moieties and a phenyl
oxazoline group. Replacement of the oxazoline with a phosphoroamidite moiety
had a negative effect on the enantioselectivity (Table 12.4, entry 1 versus 2). In
contrast to the conjugate addition to
trans
-3-nonen-2-one, yields and enantioselec-
tivities did not improve on using different catalyst precursors, solvents, and ligand-
to-copper ratios.
Chiral S,O ligands
56a-d
have also been applied to the addition of trimethyla-
luminium to
trans
-non-3-en-2-one. The best results were obtained using
[CuMeCN)
4
]BF
4
instead of Cu(OTf)
2
as a Cu source, and THF as a solvent. Conver-
sions ranged between moderate and good (40-73%), and the enantioselectivities
were between low and moderate (up to 34%). Performing the reaction at
20 °C
led to the optimum enantioselectivities (22% ee at best, Table 12.3, entry 5),
with only a slight decrease of conversion with respect to higher temperatures.
Lower temperatures (
−
−
40 °C) led to higher enantioselectivities (34% ee), but the
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