Chemistry Reference
In-Depth Information
R'
R' = Me under Ar
R' = H under Ar
under H
2
C=CH
2
91%
20%
90%
R'
Grubbs I
N
N
8.405
8.406
Ts
Ts
Scheme 8.111
of butadienes with electron-withdrawing groups in the 2-position are well known.
123
A practical issue with
these reactions is that, for terminal alkynes, higher yields and higher reactivity are obtained if the reaction
is carried out under an atmosphere of ethene, rather than an inert gas.
124
The
N
-tosyl pyrrolidine
8.405
with
a methyl substituent was formed cyclized in 91% yield using a first generation catalyst under inert gas, but
the corresponding terminal alkyne gave just 21% (Scheme 8.111). In contrast, when this reaction was carried
under ethene, a 90% yield was obtained.
Ene-yne metathesis has been employed in an elegant synthesis of stemoamide
8.415
(Scheme 8.112).
125
The starting lactam
8.407
, available itself from glutamic acid, was
N
-alkylated, then subjected to deprotec-
tion, Swern oxidation and application of the Corey-Fuchs method for installation of an alkyne by Wittig
1. NaH
1. (COCl)
2
,
DMSO, Et
3
N
2. CBr
4
, PPh
3
3.
n
-BuLi
Br
HO
EEO
O
O
2. MeOH, TsOH
N
H
8.407
8.408
H
1. LDA
2. MeOCOCl
MeO
2
C
Grubbs I
O
O
N
N
8
4
8
0
CO
2
M
e
CO
2
H
1. NaOH
2. CuBr
2
, Al
2
O
3
1. NaBH
4
, MeOH
2. NaOH
O
O
N
N
H
H
8
4
8
2
Br
O
O
+
O
O
N
N
H
H
O
O
8.413
8.414
Et
3
N
H
O
NiCl
2
, NaBH
4
O
N
H
O
8.415
Scheme 8.112
