Chemistry Reference
In-Depth Information
amino acids,
-lactams, and alkaloids. Murugan and Siva developed a new procedure
for asymmetric aziridination reactions to achieve excellent level of enantioselectivity
using new chiral phase-transfer catalysts
1f
and
4f
derived from cinchonine and cinchoni-
dine, respectively (Scheme 2C.21 ) [52] .
β
O
1f
or
4f
(10 mol %)
CO
2
t
-Bu
*
OH
CO
2
t
-Bu
t
-Bu
N
+
N
20% NaOH
aq
Toluene
Ph
Ph
1f
4f
: 79%, 94% ee (
S
)
: 56%, 88% ee (
R
)
Me
_
+
H
O
2
S
N
Br
O
Me
_
+
N
Br
O
O
2
S
Me
N
HO
N
H
CHO
HO
1f
CHO
4f
Me
Scheme 2C.21.
2C.7. STRECKER REACTION
The catalytic asymmetric cyanation of imines, Strecker reaction, represents one of the
most direct and viable methods for the asymmetric synthesis of α - amino acids and their
derivatives. Numerous recent efforts in this fi eld have resulted in the establishment of
highly effi cient and general protocols, although the use of either alkylmetal cyanide or
anhydrous hydrogen cyanide generally at low temperature is inevitable. In this regard,
we disclose the fi rst example of phase-transfer-catalyzed, highly enantioselective Strecker
reaction of aldimines using aqueous KCN based on the molecular design of chiral qua-
ternary ammonium salts
41
bearing the tetranaphthyl backbone as a remarkably effi cient
catalyst (Scheme 2C.22 ) [53] .
2C.8. AMINATION
We developed catalytic asymmetric amination of β-keto esters catalyzed by a novel
quaternary tetraalkylphosphonium bromide
42
(Scheme 2C.23 ) [54] . The reaction offers
valuable method for preparing a key intermediate for asymmetric synthesis of aldose
reductase inhibitor AS-3201 (Ranirestat) [55]. This is the fi rst successful use of chiral
quaternary tetraalkylphosphonium salt as phase-transfer catalyst in asymmetric synthe-
sis with high enantioselectivity.
