Chemistry Reference
In-Depth Information
Me
Me
Me
Me
Me
Ar
Me
N
O
O
Cl
Cl
H
N
Me
N
O
Ru
N
NHBu
N
NHBu
N
O
O
PPh
2
PPh
2
Ph
Ar
145
26
OtBu
24
⋅
1 mol % Cu(OTf)
2
C
6
H
6
O
O
2.4 mol %
26
3equiv Me
2
Zn,-30°C
10equiv 4-iodo-1-butene
10equiv HMPA,0°C
>
:
80% yield
15
1d.r.,97%ee
Et
O
2.5 mol %
145
CH
2
Cl
2
1 mol % Cu(OTf)
2
C
6
H
6
5 mol %
24
,2equivEt
2
Zn,
toluene,22°C,1h
O
+
Me
Me
⋅
OTs
81% over all yield
>
98% anti, 95% ee
Scheme 8A.87.
the desired products in good yields and moderate enantioselectivities. In subsequent
studies, they extended this reaction to the iridium catalyst system with ligand
146
[165] .
Remarkable enantioselectivity was achieved when complex aldehydes were used as the
electrophilic trapping reagents, such as benzaldehyde and
- alkoxy aldehydes.
Following Noyori's works [167], Morris and other groups [166] reported an important
rhodium catalyst
147
that was used to catalyze Michael addition of malonates to α , β -
unsaturated ketone compounds. This system allowed a one-pot tandem asymmetric
Michael addition/ketone hydrogenation protocol to create two stereogenic centers
(Scheme 8A.88 ).
Porter and coworkers [168] and Sibi and Chen [169] reported the addition of free
radicals to oxazolidinone acrylates for the creation of chiral center. For example, using
magnesium and copper salts as the catalyst in combination with a chiral bisoxazoline
148
, this reaction could give the desired products with good yields and high enantio-
selectivities (Scheme 8A.89 ).
Wang and coworkers [170] reported a new organocatalytic tandem Michael aldol
reaction that was recognized as an effi cient method for the preparation of chiral thio-
chromenes with high enantioselectivities. This reaction was mediated with catalyst
149
at room temperature and gave the product in 96% yield and 94% ee (Scheme 8A.90).
Broad range of α , β-unsaturated aldehydes and 2-mercaptobenzaldehydes could also be
tolerated in this process.
Gaunt et al. developed a catalytic enantioselective tandem conjugate addition pro-
cedure for the preparation of synthetically versatile [n.1.0]bicycloalkanes as a single
diastereoisomer. With a catalytic amount of chiral amine
150
or
151
, this reaction
afforded the desired enantiomer with high enantioselectivity (Scheme 8A.91 ) [171] .
α
