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O
O
CF
3
PhN
2
BF
4
Pd
2
(dba)
3
(10 mol%)
(o-tol)
3
P, EtOH, 40°C, 2h
CF
3
82% (Z:E = 94:6)
Scheme 9.91 Base-free arylation of 1-acyl-2-trifluoromethylethylenes.
BnO
N
2
BF
4
O
Pd
2
(dba)
3
(2.5 mol%)
M eC N, r .t ., 20 m in
83%
+
BnO
MeO
BnO
O
BnO
OMe
Scheme 9.92 Example of arylation of a protected glycal.
N
2
BF
4
Pd(OAc)
2
(5 mol%)
dioxane, 40 °C, 1 h
+
NO
2
COOMe
NO
2
H
2,
charcoal
40°C, 24 h
71%
COOMe
N
H
O
Scheme 9.93 Acid-catalysed cyclization cascaded with the base-free arylation of
a-aryl acrylates by arenediazonium salts.
Arylation of enol ethers, including cyclic compounds, nicely follows the
polar pathway paradigm.
285
Arylation of glycals is a unique route to C-aryl-
glycosides. Glycals are electron-rich internal olefins, hardly compatible with
common Mizoroki-Heck procedures. Aryldiazonium salts allowing for very
mild reaction conditions were shown by Schmidt and Biernat
286
to arylate
effectively protected glycal in a base-free reaction using only 2.5 mol%
Pd
2
(dba)
3
; more than 30 catalytic cycles run within 20 min in the increas-
ingly acidified environment (Scheme 9.92).
The base-free reaction using diazonium tetrafluoroborates generates a
strong acid, HBF
4
, which may participate as an acid catalyst in follow-up or
side reactions involving the components of the reaction system. An inter-
esting example of such behaviour was discovered by Felpin et al., who in-
vestigated a one-pot Heck arylation-hydrogenation-cyclization sequence
(Scheme 9.93).
287
In this method, o-nitrobenzenediazonium salt arylated acrylates or
a-substituted acrylates in a base-free system and the product formed was
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