Handbook of Functionalized Organometallics Applications in S

2.6 Remote Functionalized Organolithium Compounds
systems. Treatment of the iodinated methoxy compound 221 with two equivalents of
t-BuLi in heptane at ±78 C gave the e-functionalized organolithium compound
222, which upon addition of TMEDA, suffered intramolecular S N2¢ cyclization to
give the vinylcyclopropane 223 in almost quantitative yield (Scheme 2.30) [182].
I OMe
t-BuLi, n-C7H16 -78ºC
Li OMe
1. TMEDA
2. H2O 221 222 223 (93%)
Scheme 2.30
On the other hand, the silyl-substituted vinyllithium 224, prepared by bromine±lithium
exchange, did not cyclize and reacted with 3-fluoro-3-buten-2-one
to give the corresponding alcohol, which was used in the synthesis of (±)-dammarenediol
[183]. The e-oxido functionalized intermediate 225 was prepared from
the corresponding chlorohydrine by a chlorine±lithium exchange with lithium
naphthalenide after deprotonation, and reacted with iodoarenes to give the
expected coupling products [184]. The organolithium compound 226, containing
a masked acylsilane functionality, was prepared from the corresponding iodinated
precursor by treatment with t-BuLi, and reacted with substituted cyclopent-2enones
to give the expected 1,2-addition products. This strategy was used for the
synthesis of isocarbacyclin, a stable analog of prostacyclin [185].
2.6.2
Remote Allyl and Benzyllithium Compounds
The allyllithium compound 227 was generated from the phenylsulfanyl precursors
by means of lithium naphthalenide in THF at ±78 C in the presence of
TMEDA and underwent a irreversible retro- [1,4]-Brook rearrangement to give an
almost 4:1 mixture of syn,trans and anti,trans diastereomers [186].
Li
SiMe 3
OLi
Li
TMS Li
TBPSO
224 225 226 227
A diastereomeric mixture of isopentenyldimethylcyclopentanols 230 was
obtained through a lithium-ene cyclization starting from the oxido allylic intermediate
229, which was generated by LiDTBB carbon±sulfur bond cleavage of
228, the lithium oxide unit facilitating the cyclization. The corresponding magnesium
derivatives participated in the same cyclization process (Scheme 2.31) [187].
O
O
Ph
35
Li