Chemistry Reference
In-Depth Information
?
dissociation
M
coordination
M
M
fragmentation
M
M
fragmentation
M
M
M
coordination
dissociation
Scheme 8.52
Cl
N
AlMe
3
Cp
2
Ti
Cp
2
Ti
A
lMe
2
Cp
2
Ti
Cl
Cl
8.186
8.187
8.188
Scheme 8.53
O
O
O
Cp
2
TiCl
2
, AlMe
3
8.189
8.190
Scheme 8.54
conversion of the carbonyl group of esters and lactones to alkenes, a process that is not usually possible with
phosphorus-based reagents (Scheme 8.54).
The disadvantage of Tebbe's reagent in comparison to Wittig reagents, is that only a few are possible.
Tebbe's reagent is made by
-elimination from organotitanium complexes. If the chain attached to the
titanium is longer than one carbon, and is not
-hydride elimination is observed instead. The
same applies to the related Petasis reagent, Cp
2
TiMe
2
, prepared from titanocene chloride and methyl lithium
(Scheme 8.55).
56
The related benzyl, cyclopropyl (Scheme 8.56)
57
and vinyl analogues (Scheme 8.57) have
been prepared and used for the synthesis of enol ethers,
8.190
and
8.191
, and allenes
8.193
.
-blocked, then
