Chemistry Reference
In-Depth Information
1) (-)-(NMI)
2
ZrCl
2
Me
3
Al
MAO or H
2
O(1eq.
)
1) (+)-(NMI)
2
ZrCl
2
Me
3
Al
MAO or H
2
O(1eq.
)
OH
2) CH
2
=CHBr
[Pd]
2) O
2
32
31
(89% ee)
(dr = 7/1, 99% ee,
50% for two steps)
1) K
2
CO
3
,MeOH
2) 2 N HCl
1) Ac
2
O, pyridine
2) RuCl
3
•nH
2
O (10 mol %)
NaIO
4
,CCl
4
,MeCN,H
2
O
OAc
HO
2
C
O
O
33
(75%, dr = 7/1, 99% ee)
34
(100%, dr = 7/1, 99% ee)
MeO
TBDPSO
OH
36
O
O
35
9.3% from styrene, 99% ee
11% over 13 steps from styrene
dr > 50/1
Scheme 8C.12.
yield from styrene. The enantiopurity of isolated
32
was estimated to be 99% ee.
Acetylation followed by RuO
4
-catalyzed oxidative cleavage of the phenyl moiety and
subsequent hydrolysis gave 5 - acetoxy - 2,4 - dimethylpentanoic acid
33
, which was further
cyclized to afford lactone
34
in quantitative yield without epimerization. This tandem
process has also been applied to the synthesis of α , ω - diheterofunctional reduced poly-
propioates
35
and
36
, which are key components of inomycin and borrelidin, respec-
tively. After chromatographic separation of minor diastereomers, stereochemical purity
of
35
and
36
was estimated to be 99% ee and > 50:1 dr.
8C.3. ENANTIOSELECTIVE HYDROGEN - MEDIATED
C
-
C BOND FORMATION
Catalytic hydrogenation is one of the most widely used chemical reactions in research
laboratories and industries. Asymmetric hydrogenation accounts for more than half of
the industrial production of chiral compounds [23]. Since the discovery of simple cata-
lytic hydrogenation in the late 19th century, a couple of hydrogen-mediated carbon-
carbon bond-forming reactions have emerged as powerful industrial processes to produce
critical feedstock materials for chemical industry. For example, hydroformylation and
Fischer-Tropsch reactions are two of the best known hydrogen-mediated C- C bond -
forming reactions. However, further investigation into this type of reactions had to wait
until late 20th century.
Hydrogen - mediated C -C bond-forming reactions pose several challenges. The fore-
most challenging issue is the circumvention of the conventional hydrogenation. This
requires heterolytic activation of molecular hydrogen, enabling monohydride-based
catalytic cycles, wherein the C-H reductive elimination pathway is disabled. Then, an
