Chemistry Reference
In-Depth Information
O
O
O
O
O
H
H
O
H
O
H
11.166
11.167
11.168
(
i
-PrCO)
2
O
+
CHO
BrMg
O
OH
11.169
11.170
11.171
O
1. LDA
2. LiAlH
4
3. (COCl)
2
, DMSO, Et
3
N
HO
CHO
Li
11.172
11.173
O
O
O
1. Red-Al
®
; Me
3
SnCl
2.
n
-BuLi, CO
2
O
H
Ni(COD)
2
, PPh
3
H
11.168
11.167
O
1. Red-Al
®
, CuBr
2. BH
3
.THF
3. PCC
O
H
H
O
11.166
Scheme 11.57
diene
11.167
, which is related to asteriscanolide
11.166
by redox processes (Scheme 11.57).
78
The tetraene
11.168
was synthesized from acrolein using a sequence involving a highly regioselective ester enolate Claisen
rearrangement of
11.171
, and organotin chemistry to install the lactone. An intermediate, the propargylic
alcohol
11.173
, could be converted to the optically active form by a second Swern oxidation, followed by
reduction with lithium aluminium hydride in the presence of Darvon alcohol. The tetraene
11.168
underwent
stereoselective cyclization with nickel catalysis. The electron-poor double bond in the product
11.167
could
then be reduced using
in situ
copper hydride. The synthesis was completed by hydroboration-oxidation of
the remaining double bond from the less hindered face, creating the desired ketone
11.166
.
11.3.3 The [6
2] and [6
4] Cycloadditions
+
+
A small number of concerted cycloadditions of trienes are known, but the reaction is not common. A
more versatile process is the formal cycloaddition of
6
-triene complexes with alkynes, alkenes and dienes.
79
6
-triene complex
11.174
with a diene results in the formation of the bicyclo[4.1.4]
Heating or photolysis of an
