Chemistry Reference
In-Depth Information
O
O
Me
O
O
O
1.
2. K
2
CO
3
, MeI
O
O
O
Me
9.243
O
O
O
9.242
O
1. KHMDS; PhNTf
2
2.
Me
Me
IZn
Pd(dmdba)
2
,
L* =
9.129
(Ph
3
P)
4
Pd
Me
Me
O
O
9.245
9.244
pinB
Hoveyda-
Grubbs II
1. NaBO
3
, H
2
O
2.
t
-BuSH, AIBN
O
Me
H
Me
H
pinB
Me
Me
O
O
9
2
4
9
4
1. KHMDS; PhNTf
2
2.
i
-PrMgCl, CuCN,
dppfPdCl
2
i
-Pr
H
Me
H
Me
O
9.248
Scheme 9.67
cross-metathesis reaction of tetraene
9.245
established the seven-membered ring (for metathesis chemistry,
see Chapter 8). Closure of the final ring under radical conditions, and the coupling of a Grignard reagent (or
in situ
cuprate) completed the synthesis.
9.2.8 Allyl as a Protecting Group
The mild and selective nature of the palladium-catalysed allylation reaction has made it suitable for
protection.
90
Allyl ethers, esters, amines and carbamates can usually be easily formed by standard procedures.
The allyl group can be removed later by exposure to a palladium catalyst and a competitive nucleophile, “Y
−
”
(Scheme 9.68). This is an allyl transfer reaction. Commonly used competitive nucleophiles for allyl esters of
carboxylic acids include sodium 2-methylhexanoate,
91
secondary amines such as pyrrolidine (Scheme 9.69)
92
and morpholine,
93
and dimedone.
94
PdL
2
, YH
+ Y
XH +
Y
X
PdL
2
Scheme 9.68
