Chemistry Reference
In-Depth Information
Pd(0), Cu(I), Et
3
N
+
H
R
R'X
R
R'
L
2
Pd
R'X
R
R'
reductive
elimination
oxidative
addition
R'
L
2
Pd
R'
L
2
Pd
R
X
trans-
metallation
CuX
Cu
R
H
R
Et
3
NH X
Et
3
N
Scheme 2.112
I
(PhCN)
2
PdCl
2
CuI, pyrrolidin
e
+
OH
2.358
2.359
X
2.360
X = OH
1. TsCl, Et
3
N
2. MeHN(CH
2
)
2
NMe
2
2.361
X = NMe(CH
2
)
2
NMe
2
Scheme 2.113
(Ph
3
P)
2
PdCl
2
,
CuI, Et
2
NH
N
N
N
Br
2.362
2.363
Scheme 2.114
Clathculin B
2.361
, could be assembled in an efficient and straightforward manner by coupling iodide
2.358
with alkyne
2.359
(Scheme 2.113).
134
If acetylene itself is used in a Sonogashira reaction, then symmetrical disubstituted alkynes are generally
formed (Scheme 2.114).
130
Monocoupling of acetylene, or unsymmetrical decoupling, is usually achieved with
trimethylsilylacetylene, employing the TMS group to protect one terminus of the alkyne. Several Sonogashira
reactions were employed in a synthesis of Ailanthoidol
2.368
(Scheme 2.115), one employing TMS acetylene,
taking advantage of the facile cyclization of
o
-alkynyl phenols to benzofurans.
135
In practice, the final
cyclization of alkyne
2.367
could be carried out in tandem with a deprotection step to give Ailanthoidol
2.368
