Handbook of Functionalized Organometallics Applications in S

282
MeO 2C
O
I
7 Polyfunctional Zinc Organometallics for Organic Synthesis
N
O
SO2Ph I
Me 3ZnLi
Me 3ZnLi
ZnMe 2Li
N
SO 2Ph O
MeO 2C
ZnMe2Li PhCHO
OH
N
SO2Ph 174a 175a 176a :83%
O
-78 ºC
-78 ºC
25 ºC
MeO 2C
174b 175b 176b :74%
Scheme 7.53 Preparation of arylzincates via an I/Zn-exchange reaction.
I
t-Bu 3ZnLi
0ºC
R 2Cu(CN)Li 2
0ºC
O
O
O
O
177
[Zn-ate]
2-ThCu(CN)Li
178
[Cu-ate]
Scheme 7.54 Preparation of zincates on the solid phase.
PhCHO
resin cleavage
O
resin cleavage
+
MeO
MeO
O
O
N
SO 2Ph
ca. 3 %
ment of the iodomesylate 179 with Bu 3ZnLi leads to the new zincate 180 that
undergoes a 1,2-migration leading to the benzylic zinc reagent 181. It is readily
quenched with an aldehyde leading to the alcohol 182 in 80% yield (Scheme 7.55)
[130]. Interestingly, lithiumand magnesiumtriarylzincates add to a,b-unsaturated
sulfoxides in the presence of catalytic amounts of Ni(acac) 2 with good diastereoselectivity
(Scheme 7.55) [131].
7.3
Reactions of Organozinc Reagents
The high covalent degree of the carbon±zinc bond and the small polarity of this
bond leads to a moderate reactivity of these organometallics towards many electrophiles.
Only powerful electrophiles react in the absence of a catalyst. Thus, bromolysis
or iodolysis reactions are high-yield reactions. In general, a direct reaction of
OH
OH
OH
Ph
Ph
O