Chemistry Reference
In-Depth Information
SPRIX
128
, Pd(OTf)
2
p
-Benzoquinone
CH
2
Cl
2
H
H
H
i
-Pr
i
-Pr
i
-Pr
i
-Pr
OBz
N
N
O
O
O
HO
OBz
SPRIX
128
1
2
6
1
2
7
(68%, 95% ee)
Scheme 5.40.
O
O
(
−
)-Spartein, Pd(TFA)
2
DIPEA, O
2
Toluene
NH
N
H
130
(63%, 91% ee)
129
CH
3
O
O
Bisoxazoline
133
, Cu(OTf)
2
MnO
2
, K
2
CO
3
PhCF
3
NN
N
O
2
NHTs
131
Ph
Ph
132
(72%, 94% ee)
Bisoxazoline
133
Scheme 5.41.
enantioselectivity. The enantioselective oxidative cyclization of alkenyl arylsulfonamide
131
was reported by Zeng and Chemler [47c]. The reaction of
131
was catalyzed by chiral
copper(II) catalyst derived from Cu(OTf)
2
(0.2 equiv) and bisoxazoline
133
(0.2 equiv)
to give carboamination product
132
in 94% ee. The highest conversions were obtained
with MnO
2
(3 equiv) as oxidant in trifl uorotoluene as solvent. Because the use of toluene
as solvent led to the formation of both carboamination and hydroamination products,
Chemler hypothesized the formation of intermediate carbon radical and the subsequent
capture of a hydrogen atom from the solvent, giving a hydroamination product.
Tietze and others reported a new enantioselective palladium-catalyzed method for
preparation of the chiral chroman framework of vitamin E (Scheme 5.42) [48]. The
reaction of
134
with methyl acrylate
135
in dichloromethane in the presence of catalytic
amounts of Pd(TFA)
2
, (
S
,
S
) - BOXAX
137
, and
p
- benzoquinone afforded the desired
chroman
136
with 96% ee in 84% yield. The reaction was also carried out with methyl
vinyl ketone, although the selectivity was lower.
5.4.4. Related Reactions
As related reactions, electrophile-promoted addition reactions are important fi elds of
study in modern synthetic organic chemistry. Examples include organoselenylation with
chiral selenium reagents [49], iodocyclization with iodonium ion/dihydroquinine com-
plexes [50], and chlorohydroxylation with Pd(II)-BINAP complex [51].
