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i
Pr
i
Pr
P
i
Pr
N
N
N
OTMS
(20 mol%)
TMS
RCHO
+
R
THF
Scheme 5.40
1,2-Addition of allylsilane
yields were observed for aldehydes bearing electron-donating groups. For reasons not clear,
the less sterically hindered CH
3
-proazaphosphotrane proved to be ineffective for this
transformation. The reaction is assumed to proceed via activation of the allylsilane by attack
of the phosphorus atom of
i
Pr-proazaphosphatrane at the allylic silicon atom to form a
phosphonium ion, with formation of an allylic anion that then adds to the aldehydes [62]
(Scheme 5.40).
5.4.2.2 Activation of Trimethylsilyl Cyanide
The proazaphosphatrane base promotes the trimethylsilylcyanation of aryl and alkyl alde-
hydes and ketones in moderate to high yields at room temperature.
29
Si-NMR spectra
suggested that a phosphorus-silicon adduct is formed as an intermediate [63] (Scheme 5.41).
5.4.2.3
1,4-Addition of Nucleophiles
The 1,4-addition of primary alcohols, higher nitroalkanes and a Schiff
s base of an
a
-amino
a
b
ester to
-unsaturated substrates produces the corresponding products in moderate to
excellent yields in the presence of catalytic amounts of the nonionic strong bases
P(RNCH
2
CH
2
)
3
N in isobutyronitrile. Diasteroselectivity for the anti form of the product
is higher than in the case of the Schiff
s base in the absence of lithium ion [64]
(Scheme 5.42).
,
5.4.2.4
a
-Arylation of Alkanenitriles
A new catalyst system for the synthesis of
-aryl substituted nitriles has been reported. The
i
Bu-proazaphosphatrane serves as an efficient and versatile ligand for the palladium
a
P
Me
Me
Me
N
N
N
CN
R
(10 mol%)
RCOR'
+
TMSCN
T
S
R'
Scheme 5.41
1,2-Addition of trimethylsilylcyanide
