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PMBO
CO
2
Me
PMBO
CO
2
Me
(a) (Ph
3
P)
3
RhCl, DABCO, 16 h;
(b) HgCl
2
,HgO,90min.
100%
O
O
BnO
BnO
OH
BnO
BnO
O
PMBO
CO
2
Bn
PMBO
CO
2
Bn
(a) (Ph
3
P)
3
RhCl, DABCO, 16 h;
(b) HgCl
2
,HgO,90min.
100%
O
O
BnO
BnO
OH
BnO
BnO
O
FIGURE 1.24
Barbier et al.'s [42] two-step method to remove the allyl group from
allyl galactopyranosiduronic acid derivatives using DABCO and (Ph
3
P)
3
RhCl followed by
mercuric-assisted cleavage.
Sharma et al. [45] describe a novel, zirconium chloride-based methodology
enabling a highly selective deprotection of
t
-butyldimethylsilyl (TBS) ethers in the
presence of
t
-butyldiphenylsilyl (TPS) ethers. Figure 1.27 shows the only carbohy-
drate example from the paper. Other examples are equally impressive. While the
difference between the TPS and TBS ethers seems to be very minute, one can accom-
plish a spectacular selectivity in deprotection of these species. However, without
BnO
HO
OBn
OH
BnO
O
HO
O
BnO
HO
95%
OMe
OMe
TBDMSO
TBDMSO
OBn
OH
BnO
HO
O
O
BnO
HO
95%
OMe
OMe
HO
Ph
O
OAc
OAc
HO
O
O
O
AcO
AcO
95%
OMe
OMe
HO
Ph
O
OBn
OH
O
HO
O
O
BnO
HO
90%
OMe
OMe
FIGURE 1.25
Application of flow chemistry to deprotection of benzyl-/benzylidene-
protected carbohydrates [43].
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