Handbook of Functionalized Organometallics Applications in S

O Li O Li O Li
4 ent-4 5 6
O Li
N O R
It is possible to transform stereoselectively the anomeric position of a sugar
unit into a organolithium compound by chlorine±lithium exchange using a stoichiometric
amount of lithium naphthalene as the lithiating reagent [13]. The
same kind of intermediates were prepared also by tin±lithium transmetallation
[14] and sulfur±lithium exchange in phenyl sulfides and sulfones [15]. In the case
of the dianion 8 derived from galactopyranose, the deprotonation of the amide
moiety in compound 7 should be performed prior to heteroatom±lithium
exchange. The reaction of this intermediate with electrophiles provided a-C-glycosides
9 (Scheme 2.2).
BnO
OBn
BnO
O
AcHN
Cl
[E = MeOD, RCHO, CO 2]
Scheme 2.2
1. n-BuLi, THF, -90ºC
2. LiC10H8 (2.2 equiv), -90ºC
BnO
OBn
BnO
O
AcLiN
Li
1. E
2. NH 4Cl-H 2O
BnO
OBn
BnO
O
AcHN
X
7 8 9 (72-86%)
High diastereoselectivity was observed in the reaction of intermediate 11 (prepared
by tin±lithium exchange from compound 10, which derived from L-valine)
with benzaldehyde to give the corresponding adducts in a 91:9 diastereomeric ratio.
Final hydrolysis yields the 1,2-diol 13 and the chiral auxiliary 12 (Scheme 2.3) [16].
O Ph
Scheme 2.3
O SnBu 3
n-BuLi (2 equiv)
THF/Et2O, -78ºC
10 11
OH O
Ph
2.2 a-Functionalized Organolithium Compounds
+
Ph
O Ph
OH
O Li
OH
12 13 (91%)
1. PhCHO, -78ºC
2. CSA, MeOH, rt
Compounds 14[11]-18 have also been prepared from the corresponding stannanes.
Surprisingly, cyclic a-alcoxy-b-aminoalkyllithium compounds 15 and 16
9