Biomedical Engineering Reference
In-Depth Information
Me
O
N
Ph
Me
H
Me
Me
·TFA
106
(20 mol%)
H
H
CAN, NaHCO
3
TMS
+
O
DME
-20°C, 24 h
75%
O
107
(ee = 94%)
104
105
SCHEME 6.20
Organocatalytic
a
-allylation of aldehyde under SOMO activation.
to create a transient radical species [38]. Hence, enantioselective
a
-allylation of
cyclohexylacetaldehyde (
104
) was achieved with allyltrimethylsilane (
105
) in the
presence of a catalytic amount of chiral amine
, ceric ammonium nitrate (CAN),
and NaHCO
3
in water-containing dimethoxyethane (DME) and afforded the
a
-allylaldehyde
106
in high enantioselectivity (Scheme 6.20). Enantioselective
heteroarylations and cyclization/halogenation cascades were also performed under
SOMO activation [38].
In addition to the
a
-allylation, the
a
-vinylation of cyclohexylacetaldehyde was
established using vinyl trifluoroborate salt
107
108
instead of allyltrimethylsilane (
105
)
(Scheme 6.21) [39].
Nicolaou et al. applied the enantioselective intramolecular Friedel-Crafts-type
a
-arylation of aldehyde
110
111
to prepare the corresponding cyclized product
, which
112
was then transformed into demethyl calamenene
(Scheme 6.22) [40].
The enantioselective organo-SOMO catalysis was successfully used in the
cyclization of the polyunsaturated aldehyde
113
to afford the corresponding poly-
cyclic product
115
in high enantioselectivity (Scheme 6.23) [41].
Ph
106
(20 mol%), CAN
H
2
O, NaHCO
3
H
H
Ph
+
KF
3
B
DME, -50°C, 24 h
82%
O
O
109
(ee = 96%)
104
108
SCHEME 6.21
Organocatalytic
a
-vinylation of aldehyde under SOMO activation.
106
(20 mol%)
CAN, H
2
O
MeO
MeO
MeO
DME
-30°C, 24 h
56%
Me
Me
Me
CHO
CHO
Me
Demethyl calamenene (
112
)
Me
110
111
(ee = 90%)
SCHEME 6.22
Friedel-Crafts-type
a
-arylation of aldehyde.
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