Chemistry Reference
In-Depth Information
OCO
O
CO
2
Pd(OAc)
2
, (
i
-PrO)
3
P
O
CO
2
Et
CO
2
Et
9.195
PdL
2
9.196
O
O
O
O
O
O
CO
2
Et
CO
2
Et
9.197
9.198
PdL
2
Scheme 9.55
The alkoxide released is also nucleophilic and may be trapped with electrophiles such as CO
2
and iso-
cyanates prior to attack on the
-allyl complex (Scheme 9.55). The attack of the alkoxide on CO
2
generates
a hemicarbonate
9.197
, which can close back on the
-allyl complex.
The isocyanate trapping method was employed in a synthesis of an unusual sugar, acosamine
9.209
, as its
O
-methyl,
N
-acetyl derivative (Scheme 9.56).
71
The substrate for the palladium chemistry was prepared from
methyl lactate
9.199
, which is readily and cheaply available as its (
S
)-enantiomer. The alcohol was protected,
1. (MeO)
2
P(O)CH
2
CO
2
Me,
LiCl,
i
-Pr
2
NEt
2. DIBAL
1. TBSCl, Et
3
N
2. DIBAL
CHO
CO
2
Me
OH
TBSO
9.199
9.200
O
1. (COCl)
2
, DMSO,
Et
3
N
2. Ph
3
P=CH
2
Ti(O
i
-Pr)
4
, (+)-DET,
t
-BuOOH
OH
OH
TBSO
TBSO
9.201
9.202
O
O
O
O
NTs
(dba)
3
Pd
2
.CHCl
3
P(O
i
-Pr)
3
, TsNCO
O
NTs
TBSO
TBSO
TBSO
PdL
2
9.204
9.203
9.205
O
O
1. Na C
10
H
8
2. R
2
BH;
H
2
O
2
, NaHCO
3
O
1. PCC, CH
2
Cl
2
2. (Me
3
O)
3
CH,
MeOH, PPTS
O
NH
NTs
OH
TBSO
TBSO
9.206
9.207
O
1. NaOH,
Δ
OMe
O
2. Ac
2
O
3. MeOH, H
+
NH
OMe
O
HO
AcHN
TBSO
OMe
9.209
9.208
Scheme 9.56
