1.2 C–H Activation
7
N
HO
Na 2 [PdCl 4 ]
(1.00 equiv)
NaOAc
(1.02 equiv)
2 L
L = pyridine,
PMe 2 Ph,
PPh 3
N
HO
OAc
O
OAc
2
Pb(OAc) 4
(1 equiv)
Pb(OAc) 4
(2 equiv)
then NaBH 4
N
HO
2
Pd
Cl
N
HO
Pd
L
Cl
N
HO
Pd
Py
Cl
(a)
9
1 0
11
(b)
11a
12
13
Scheme 1.4: Stoichiometric C–H bond oxidation. (a) The synthesis of monomeric palladacycle 11. (b) Baldwin’s cyclopalladation method.
the Pb(OAc) 4 promoted oxidation was followed by reduction of Pd
II to Pd
0
with NaBH 4 .
Baldwin’s cyclopalladation reaction has found wide application in the synthesis and modification of natural products and their analogues.Baldwin et al.
used it for derivatisation of the triterpene lupanone (14) (Scheme 1.5a).
[25]
Carr et al. used the method to introduce a hydroxy group at C-23 of lanostenone (16), enabling 4α-demethylation to obtain 4β-demethyl-lanostenone (17)
(Scheme 1.5b).
[27] Peakman et al. applied Baldwin’s method for the introduction of a hydroxy group at C-23 of ursenone oxime, oleanenone oxime and
lupanone oxime.
[28] Bore et al. have utilised it in the transformation of ursolic
acid (18) into β-boswellic acid analogues (19a,b) (Scheme 1.5c).
[29] Finally,
as described in Section 1.1.3, Wen et al. have employed this method for
introduction of the C-23 hydroxy group in their semisynthesis of hederagonic
acid (1) (Scheme 1.5d).
[1]
7
N
HO
Na 2 [PdCl 4 ]
(1.00 equiv)
NaOAc
(1.02 equiv)
2 L
L = pyridine,
PMe 2 Ph,
PPh 3
N
HO
OAc
O
OAc
2
Pb(OAc) 4
(1 equiv)
Pb(OAc) 4
(2 equiv)
then NaBH 4
N
HO
2
Pd
Cl
N
HO
Pd
L
Cl
N
HO
Pd
Py
Cl
(a)
9
1 0
11
(b)
11a
12
13
Scheme 1.4: Stoichiometric C–H bond oxidation. (a) The synthesis of monomeric palladacycle 11. (b) Baldwin’s cyclopalladation method.
the Pb(OAc) 4 promoted oxidation was followed by reduction of Pd
II to Pd
0
with NaBH 4 .
Baldwin’s cyclopalladation reaction has found wide application in the synthesis and modification of natural products and their analogues.Baldwin et al.
used it for derivatisation of the triterpene lupanone (14) (Scheme 1.5a).
[25]
Carr et al. used the method to introduce a hydroxy group at C-23 of lanostenone (16), enabling 4α-demethylation to obtain 4β-demethyl-lanostenone (17)
(Scheme 1.5b).
[27] Peakman et al. applied Baldwin’s method for the introduction of a hydroxy group at C-23 of ursenone oxime, oleanenone oxime and
lupanone oxime.
[28] Bore et al. have utilised it in the transformation of ursolic
acid (18) into β-boswellic acid analogues (19a,b) (Scheme 1.5c).
[29] Finally,
as described in Section 1.1.3, Wen et al. have employed this method for
introduction of the C-23 hydroxy group in their semisynthesis of hederagonic
acid (1) (Scheme 1.5d).
[1]