_P.-Powell-auth.-Principles-of-Organometallic-Chemistry-Springer-Netherlands-1988

The first three periodic groups
H H
Et -Ct-~oR BuLi/ E '--OR
, t-e-- + Bu Sn
' THF, -78° "- 4
SnBu3 U
( e) DILITHIO DERIV ATIVES. 1, 1-Dilithiomethane has been obtained by pyrolysis
of pure, salt free methyllithium (p. 3 5). The direct reaction between lithium
metal and dibromomethane gives only about 6% yield. A two step synthesis
through a dimercury derivative is more successful.
CH,l,
Hg
~ CH,(Hgi),
--c
CH,Li,
4Li
4Bu'Li
+ 2Hg + 2Lil
CH,Li, + Bu~Hg + 2Lii
The preparation of 1, 1-dilithioethane illustrates several general organometallic
reactions, including hydroboration and the transfer of organic groups from
one element to another. Dilithioethane is rather susceptible to decomposition into
vinyllithium and lithium hydride through /3-hydrogen transfer.
H2C=CH8r Mg/THF H C=CHM Br (i)B(OMe)3 H C=CHB(OBu") (i)H3B.THF
2 g (ii)Bu"OH 2 2 (ii}Bu"OH
3.3.2 Reactions of organolithium compounds and comparison with
Grignard reagents
(a) GENERAL REACTIVITY. Some reactions of organolithium compounds
which illustrate their great versatility in synthesis are summarized in Fig. 3.8.
The reactions ofthe corresponding and less reactive Grignard reagents (p. 50) are
often similar. Grignard reagents, for instance, do not metallate alkenes or arenes,
although they do exchange with alkynes. Nucleophilic attack by Grignard and
organolithium reagents on multiple bonds such as ) C=O or -C=N leads after
hydrolysis to a wide range of organic products. It is generally most convenient to
use the Grignard reagents to effect these classical transformations, as less rigorous
precautions are required. In a few instances, however, organolithium reagents
behave differently. Carboxylate salts, for example, react as follows:
44
stoble to ottock
by R'Li