Handbook of Functionalized Organometallics Applications in S

370
8 Polyfunctional 1,1-Organodimetallic for Organic Synthesis
Optically active epoxides were treated with bis(iodozincio)methane 4. From 33,
34 was obtained in an optically active form, though a slight decrease of the enantiometric
purity was observed (Scheme 8.41). The remarkable point of the transformation
is the absolute configuration of the product. The migrating group,
-CH 2OH, came from the front side of the C±O bond. It is an unusual retentative
migration reaction. For example, Yamamoto and Maruoka had reported the pinacolone
rearrangement of the silyl ether of 33 with MABR (methylaluminum bis(4bromo-2,6-di-tert-butylphenoxide)
[44b]. The rearranged product 36 was treated
with 4 to convert into alkene. After desilylation, the obtained homoallylic alcohol
37 was an enantiomer of 34.
8.2.10
gem-Dizincio Reagent Working as Carbenoid
Bis(iodozincio)iodomethane was prepared from diethylzinc and iodoform as
shown in Scheme 8.42 by Charette. The prepared 38 possesses a potential both as
a carbenoid and as a gem-dimetal, and reacts as a zinciomethyl carbenoid as
shown in Scheme 8.43 [45].
Et2Zn + CHI3 I
ZnI
ZnI
38
Scheme 8.42 Preparation of bis(iodozincio)iodomethane.
OBn
OBn
38
IZn
39
OBn
OBn
Scheme 8.43 Preparation of cyclopropyl zinc.
1) CuCN 2LiCl
2) E +
E
OBn
OBn
E + : allyl bromide 85%
benzoyl chloride 84%
As shown in Scheme 8.43, benzyl ether of cis-2-buten-1,4-diol is treated with 38
to give cyclopropylzinc intermediate 39 that reacts with various electrophiles. The
obtained cyclopropyl derivative has all cis configuration. In this reaction, zinc
halide that exists in the reagent solution played an important role [45, 46].