O-Glycosyl Donors
3.4
585
( > Scheme 14a) [70]. By contrast, good results were obtained with the benzylidenated derivative 110 ( > Scheme 14b). The authors ascribed this result to the conformational constraint
imposed by the benzylidene ring, in keeping with their precedents [41].
Svarovsky and Barchi [71] observed a striking reactivity difference between pent-4-enyl β- and
α-2-azido-2-deoxy galactosides 113 and 116, respectively ( > Scheme 14c-X). Thus, where⊡ Scheme 15
Pent-4-enyl 2-allyloxycarbonyl-2-deoxy-D- and L-glucopyranosides
⊡ Table 4
Glycosidation of (−)-menthol (125) by oxazolidinone protected NPGs, 124
Entry
Oxazolidinone
R a
IDCP (equiv)
α:β
Yield (%)
i
α
H
2
4:1
53
ii
β
H
2
5:1
24
iii
α
CBz
4
α only
71
iv
β
CBz
4
α only
4
v
α
TCBoc
4
α only
41
vi
α
Troc
4
α only
50
vii
α
Boc
4
α only
63
a CBz = (benzyloxy)carbonyl, TCBoc = (2,2,2-trichloro-1,1-dimethylethoxy)carbonyl,
Troc = (2,2,2-trichlroethoxy)carbonyl, Boc = tert -butoxycarbonyl
3.4
585
( > Scheme 14a) [70]. By contrast, good results were obtained with the benzylidenated derivative 110 ( > Scheme 14b). The authors ascribed this result to the conformational constraint
imposed by the benzylidene ring, in keeping with their precedents [41].
Svarovsky and Barchi [71] observed a striking reactivity difference between pent-4-enyl β- and
α-2-azido-2-deoxy galactosides 113 and 116, respectively ( > Scheme 14c-X). Thus, where⊡ Scheme 15
Pent-4-enyl 2-allyloxycarbonyl-2-deoxy-D- and L-glucopyranosides
⊡ Table 4
Glycosidation of (−)-menthol (125) by oxazolidinone protected NPGs, 124
Entry
Oxazolidinone
R a
IDCP (equiv)
α:β
Yield (%)
i
α
H
2
4:1
53
ii
β
H
2
5:1
24
iii
α
CBz
4
α only
71
iv
β
CBz
4
α only
4
v
α
TCBoc
4
α only
41
vi
α
Troc
4
α only
50
vii
α
Boc
4
α only
63
a CBz = (benzyloxy)carbonyl, TCBoc = (2,2,2-trichloro-1,1-dimethylethoxy)carbonyl,
Troc = (2,2,2-trichlroethoxy)carbonyl, Boc = tert -butoxycarbonyl