Chemistry Reference
In-Depth Information
O
Ar
N
HO
O
R = H
85% (98% ee)
R
O
R
O
N
Bn
Bn
+
N
Ar
H
N
HO
O
OH
12
O
(10 mol%)
87% (97% ee)
Ar = 2-NO
2
-C
6
H
4
R = OH
O
N
O
Ar
Scheme 4.12
TMG (1) catalysed reaction between anthrone and succinimide
Diels-Alder Reaction
A chiral bicyclic guanidine 12 was found to be an excellent catalyst for Diels-Alder
reactions between anthrones and various dienophiles [35]. The catalyst can torelate a range
of substituents and substitution patterns, making several anthrone derivatives suitable for
this reaction. The use of 1.8-dihydroxy-9-anthrone as an anthrone substrate led to the
production of 5-substituted anthrone as a Michael adduct in excellent yields, high
regioselectivities and high enantioselectivities (Scheme 4.12).
4.3.1.5 Cyanosilylation
TMG (1) acts as a highly effective catalyst for the cyanosilylation of various ketones and
aldehydes to the corresponding adduct in high yields. The reaction proceeds smoothly with
0.1mol% catalyst loading at 25
C without solvent [36].
Treatment of aldehydes and trimethylsilyl cyanide (TMSCN) in toluene at
78
Cinthe
presence of the catalytic amount of symmetrical bicyclic guanidine 13 smoothly afforded an
(S)-excess adduct with good to moderate ee [37]. (Table 4.3) A ketonic 3-phenyl-2-butanone
canwork as an acceptor under the above conditions, but reactivity is low (23%yield, 39%ee).
Table 4.3
Asymmetric TMS cyanation of aldehydes catalysed with guanidine 13
13
TMSO
(0.1 equiv)
H
Ph
R-CHO
(1 equiv)
TMSCN
(1.5 equiv)
+
R
CN
toluene
-78 ºC
N
Ph
H
Run
R
Time (h)
Yield (%)
ee (%)
NN
1
Ph(CH
2
)
2
-
6
85
50
2
cyclohexyl
1.5
93
70
Ph
Ph
t
Bu-
3
7
92
43
13
