Chemistry Reference
In-Depth Information
R
R
[Pd(MeCN)
4
](BF
4
)
2
(5 mol %)
(
S
)-BINAP (10 mol %)
HCOOH (1 eq.)
Ts
Ts
DMSO, 100°C, 1-3 h
R = H
R = CO
2
Me
>99% ee (99%)
>99% ee (99%)
N
Ts
15
15
[Pd(MeCN)
4
](BF
4
)
2
(5 mol %)
(
S
)-BINAP (10 mol %)
HCOOH (1 eq.)
Ts
DMSO, 100°C, 1 h
86% ee (53%)
Scheme 8D.54.
The enantioselective quinoline cyclization to construct quaternary centers challenged
four - , fi ve - , and fi fteen-membered spiro-ring cyclization. Especially with the terminal
acetylenic substrate with fi fteen - membered olefi n, the olefi n-migrated spiro product is
obtained in moderate yield (53%) but with high enantioselectivity (86% ee).
Late transition, metal-catalyzed asymmetric addition reactions of active methylene
compounds to alkene or alkyne system are generally called as the Conia-ene reaction
[85]. The enantioselective catalysis of the
-vinylation of carbonyl compounds to provide
all carbon quaternary centers is attained by late transition metal catalysts such as chiral
Pd(II) complexes (Scheme 8D.55) [86]. Chiral Pd(II) complexes with DTBM-SEG-
PHOS catalyze the Conia-ene cyclization to provide
α
- vinyl ketone compounds. The
highly enantioselective version has been attained by the combined use of Yb(OTf)
3
in
dilute diethyl ether solution (0.02 M) to provide high yield and enantioselectivity.
α
8D.7. D - A - TYPE REACTION
Recent successes in asymmetric intra- and intermolecular (hetero) D-A-type reactions
catalyzed by chiral metal complexes are discussed. Chiral organocatalyst-catalyzed (such
as proline, imidazolidinone, and Brønsted acid) reactions are reported in Chapter 2A
by Watson and MacMillan and Chapter 3 by Yamamoto and Cheon.
8D.7.1. Intramolecular [4 + 2] Cycloaddition
Transition metal-catalyzed D-A reactions [87] of unactivated dieneynes such as intra-
molecular [4 + 2] cycloaddition are powerful synthetic methods leading to 5,6- or 6,6-
