Chemistry Reference
In-Depth Information
1. (Ph
3
P)
4
Pd, LiCl
2. DIBAL
3. Dess-Martin
4. HF.pyridine
CHO
O
I
N
N
N
N
OTES
OH
PMBO
HO
2.181
2.182
SnBu
3
Scheme 2.63
O
CO
2
Bn
O
2.183
2.185
1. KOH
2. TBDPSCl, C
3
H
4
N
2
3. (COCl)
2
n
-Bu
3
SnH, AIBN
O
n
-Bu
3
Sn
Cl
CO
2
Bn
TBDPSO
2.184
2.186
CO, BnPd(PPh
3
)
2
Cl
O
CO
2
Bn
TBDPSO
2.187
Scheme 2.64
O
O
O
Cl
CO, BnPd(PPh
3
)
2
Cl
O
O
O
O
O
Sn
n
-Bu
3
O
2.188
2.189
Scheme 2.65
of CO.
65
Le Chatelier's principle then operates to disfavour decarbonylation. This method was used in a
synthesis of a pyrenophorin precursor
2.187
(Scheme 2.64).
66
Another approach to the same natural product, pyrenophorin
2.189
, is to carry out a dimerization by the
Stille coupling of a stannane containing an acid chloride
2.188
(Scheme 2.65).
67
The fact that these two
functional groups can be in the same molecule illustrates further the functional group tolerance of the Stille
reaction. Once again, decarbonylation is prevented by the use of a CO atmosphere.
A corollary of this is that if a Stille coupling of a vinyl or aryl halide is carried out under an atmosphere of
CO, then a ketone will be produced. This is discussed in Section 4.1.
