Handbook of Functionalized Organometallics Applications in S

Li OTBS Li
OTBS
173 174
Li
Li
2.4 c-Functionalized Organolithium Compounds
N
Li
O
O
Li
175 176 177
b-Chloro E-a,b-unsaturated ketone acetals 178 underwent stereoselective
DTBB-catalyzed lithiation to give vinyllithium derivatives 179, which after reaction
with electrophiles and final acidic hydrolysis led to regioselectively functionalized
a,b-unsaturated carbonyl compounds 189. In the reaction of enantiomerically
enriched starting materials 180 (R 2 = Me) with prostereogenic carbonyl compounds,
no diastereoselectivity was observed (Scheme 2.24) [111,151].
R 2
R 2
Cl R1 O O
Li, DTBB (4%)
THF, -90ºC
[E = H 2O, D 2O, R 3 R 4 CO]
Scheme 2.24
R 2
R 2
Li R1 O O
1. E
2. H2O 3. (CO2H) 2-H2O CH2Cl2,silicagel Li
X R 1
178 179 180 (43-90%)
Aryllithium compounds of type XVIII are generated mainly either by direct deprotonation
[71,104] or by halogen±lithium exchange [75,105]. In the case p-methoxybenzaldehyde
dimethyl acetal, ortho lithiation with n-BuLi (to give the intermediate
181), followed by reaction with electrophiles and final acidic hydrolysis,
led to polyfunctionalized benzaldehydes in high yields [152]. Vinyllithium derivatives
182 and 183 (of type XIX) have been prepared from the corresponding
vinylic halides by treatment with t-BuLi. The silyl ether derivative 182 was used
in the synthesis of the C1 alkyl side chains of Zaragozic acids A and C [153] and
the intermediate 183 was involved in the total synthesis of marine metabolites
(+)-calyculin A and (±)-calyculin B [154]. The chlorovinyllithium derivative 184
was accessible through a tin±lithium transmetallation and used in the synthesis
of the marine sesquiterpenoid (±)-kelsoene [155]. Cyclic vinyllithium intermediate
185 was used in the construction of seco-taxanes, being prepared from the corresponding
ketone trisylhydrazone applying the Shapiro reaction [156].
MeO
OMe
Li
181
OMe
Li Li O O
OTBS
Cl
Li
182 183 184 185
Iron-catalyzed carbolithiation of the internal alkyne 186, bearing an alkoxy
group at the homopropargylic position, led to the vinyllithium compound 187,
Li
O
OBn
29
NOMe