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LnPd(II)
PPh
3
OPPh
3
137
136
LnPd(0)
reductive
el i m i na t io n
I
oxidative
addition
F
Pd
(II) Ln
F
N
N
Cl
Pd
(II)Ln
Cl
concerted
metallation-
deprotonation
N
Cl
Cl
II
IV
N
O
135
,AcO
O
via
N
N
N
[Pd]
Cl
N
H
O
O
III
R
Scheme 15.31 Proposed mechanism for the coupling of 135 and 136.
but they provided lower in situ yields] under a nitrogen atmosphere was
heated at reflux for 16 h (85% conversion; longer reaction times did not
increase the conversion, presumably due to catalyst decomposition).
Toluene, water and concentrated HCl were added to extract the HCl salt of
137 into the aqueous phase. After two toluene washes to remove non-basic
organic impurities, pH adjustment of the aqueous layer to 1 precipitated the
HCl salt of 137, which was collected by filtration; 137
HCl was then taken up
in a 2-MeTHF-water mixture and the pH was increased to 10-12 with 50%
NaOH to extract 137 into the organic layer. After further extractions of the
aqueous layer with 2-MeTHF, the combined organic extracts were dried and
concentrated. Purified 137 was then isolated after recrystallization from
toluene-heptane in 50% yield. No information was provided about the level
of residual Pd in 137 or API 138.
15.3 Carbon-Heteroatom Bond Formation
15.3.1 Carbon-Nitrogen Bond Formation
15.3.1.1 Copper-Catalyzed C-N Bond Formation
The traditional conditions for the copper-catalyzed Ullmann condensation
required stoichiometric copper and harsh conditions that would be in-
compatible with today's
complex molecular
structures
found in
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