Chemistry Reference
In-Depth Information
O
CHO
Rh(dppe)
2
ClO
4
3.61
3.62
Scheme 3.29
O
O
H
[Rh(S,S-Meduphos)(acetone)
2
] PF
6
3.64
3.63
Scheme 3.30
O
H
H
OHC
Rh(dppe)
2
OTf
H
H
3.65
3.66
Scheme 3.31
CHO
O
OH
H
H
MeO
2
C
MeO
2
C
Rh(dppe)
2
ClO
4
MeO
2
C
MeO
2
C
H
H
3.69
3.67
3.68
Scheme 3.32
sense, this leads to a cyclic ketone
3.62
(Scheme 3.29).
28
The reaction is more efficient using cationic
rhodium complexes with bidentate ligands,
29
although other metals, such as cobalt
30
can also be employed.
Replacement of the phosphine ligands with chiral ligands can result in the formation of a new stereogenic
centre in an asymmetric cyclization (Scheme 3.30).
31
Variations on the theme include the use of vinylcyclopropanes
3.65
(compare Scheme 11.48 and others in
Chapter 11) for the synthesis of eight-membered rings
3.66
(Scheme 3.31),
32
and polyene substrates, as in a
synthesis of epiglobulol
3.69
(Scheme 3.32).
33
Intramolecular reactions with both alkenes and alkynes can also be achieved under correctly chosen
conditions, especially when the aldehyde contains a second donor atom that can chelate the rhodium, as in
the
-thioaldehyde
3.70
(Scheme 3.33).
34
Ruthenium catalysts have been used with dienes (Scheme 3.34).
35
