Chemistry Reference
In-Depth Information
ligand (DPPF or racemic BINAP) and a stoichiometric amount of 1,1,3,3-tetramethyl-
hydrosiloxane (TMDS) in THF smoothly promoted the reaction of ketoalkyl acrylates
80
, affording the cyclic aldol products
81
with excellent diastereoselectivity (
>
95:5) in
fairly good yields (Scheme 8C.33 ) [50] .
R
2
O
O
Cu(OAc)
2
•H
2
O
Diphosphine
R
2
PPh
2
R
1
O
O
Fe
R
1
R
3
n
TMDS, THF, rt
n
=1,2
R
3
n
PPh
2
OH
80
O
DPPF
81
Scheme 8C.33.
Several chiral diphosphine ligands were screened for enantioselective reactions of
selected
82
, and it was found that (
R
) - 3,5 - xyl - MeO - BIPHEP and (
S
) - Segphos gave the
best results (i.e.,
80% ee) (Scheme 8C.34) [66]. It appears that the reaction is sensitive
to the substitution pattern and ring size. Thus, further investigation deems necessary to
be practical.
>
O
O
Cu(OAc)
2
•H
2
O (5 mol %)
Ligand (5 mol %)
TMDS, THF, rt, 24 h
R
1
O
R
1
O
2
HO
O
83
82
R
1
Ligand Yield (%) % ee
71
61
73
68
79
60
83
80
82
q
80
q
73
q
72
q
p
-Cl-Ph (
R
)-3,5-xyl-MeO-BIPHEP
PhCH
2
CH
2
(
R
)-3,5-xyl-MeO-BIPHEP
p
-Cl-Ph (
S
)-Segphos
PhCH
2
CH
2
(
S
)-Segphos
p
-Cl-Ph (
S
)-BINAP
PhCH
2
CH
2
(
S
)-BINAP
q
enantiomer opposite to that depicted.
O
O
MeO
MeO
P(3,5-xyl)
2
P(3,5-xyl)
2
PPh
2
PPh
2
O
O
(
S
)-SEGPHOS
(
R
)-3,5-xyl-MeO-BIPHEP
Scheme 8C.34.
