Chemistry Reference
In-Depth Information
Me
OH
HO
OMe
PA
1i
(5 mol %)
AcOH (1.2 eq)
Toluene, -78°C
N
N
Me
TMSO
Ar
O
Ar
H
9 examples
72-100% yield
76-91% ee
Me
OH
HO
OMe
PA
1i
(5 mol %)
N
N
Me
Toluene, -78°C
TMSO
Ph
O
Ph
H
Without AcOH: 29% yield, 34% ee
With AcOH: 78% yield, 67% ee
Scheme 3.38.
1) PA
1j
(3 mol %)
py (3 mol %)
-78°C
OH
HO
OTMS
OMe
mesitylene
MeO
+
N
N
2) PhCO
2
H (1 eq)
OMe
R
O
R
16 examples
63-91% yield
92-99% ee
Scheme 3.39.
acid. Akiyama and coworkers disclosed that phosphoric acid is effective for the aza-D-A
reaction of Brassard's diene [66]. The use of the pyridinium salt of the phosphoric acid
1j
improved the chemical yield, supposedly because use of less acidic pyridinium salt
suppressed lability of Brassard's diene in the reaction media (Scheme 3.39).
The inverse electron - demand aza - D - A reaction of electron - rich alkenes with 2 - aza
dienes was reported by Akiyama and coworkers [67]. Tetrahydroquinoline derivatives
were obtained in favor of the
cis
-isomers with excellent enantioselectivities. Because the
existence of OH group is crucial for this reaction, the authors proposed a nine-mem-
bered cyclic transition state, which was previously proposed for their Mannich and
hydrophosphorylation reactions (Scheme 3.40 ).
The groups of Gong [68] and Rueping [69] independently developed direct aza-D-A
reactions of aldimines with cyclohexenone to afford isoquinuclidines in good
endo
/
exo
selectivity and high yields and enantioselectivities, respectively (Scheme 3.41). While
Gong employed only H
8
- BINOL - derived PA
2c
, Rueping used chiral Brønsted acid PA
1l
or
lm
in combination with acetic acid. Rueping proposed double Brønsted acid cata-
lyzed activation of an electrophile (by a stronger Brønsted acid) and a nucleophile (by
