Chemistry Reference
In-Depth Information
H
OH
O
PdCl
2
, SnCl
2
,
n
-Bu
3
P, CO
O
H
4.105
4.106
H
OH
O
PdCl
2
O
4.105
CO
H
4.106
HCl
O
H
O
O
O
PdX
H
PdX
4.108
4.107
insertion
Scheme 4.42
Me
Me
Me
Ru
3
(CO)
12
,
Et
3
N
OHC
SnCl
2
, NaI,
H
2
O, DMF
HO
O
Br
•
4.109
4.110
4.111
O
Scheme 4.43
-methylene lactones
4.106
using palladium-catalysed carbonylation
(Scheme 4.42).
41
The reaction is proposed to proceed via formation of an acyl palladium species
4.107
, which
undergoes intramolecular alkyne insertion. Protonolysis of the carbon-palladium bond of the vinyl complex
4.108
yields the product.
Allenols may be carbonylated under quite different conditions. Using Ru
3
(CO)
12
as the catalyst, unsaturated
lactones can be synthesized efficiently.
42
The reaction may also be extended to lactams.
43
This cyclization,
combined with an intramolecular propargylic Barbier reaction has been used in syntheses of mintlactone
4.111
from allenol
4.110
(Scheme 4.43)
44
and its diastereoisomer, isomintlactone,
45
as well as the
stemona
alkaloid, stemoamide
4.115
from allenol
4.113
(Scheme 4.44),
46
and in the skeleton of stenine.
47
A different
synthesis of stemoamide can be found in Chapter 8, Scheme 8.112.
Alkynols
4.105
may be cyclized to
4.4 Hydroformylation
Hydroformylation is the addition of one molecule of hydrogen and one of carbon monoxide across an
alkene to generate an aldehyde (Scheme 4.45). Unsymmetrically substituted alkenes can give mixtures of
linear and branched aldehydes,
4.116
and
4.117
. Hydroformylation was discovered in the 1930s and rapidly
