CLICKING SUGARS ONTO SUGARS: OLIGOSACCHARIDE ANALOGS AND GLYCOCLUSTERS ON CARBOHYDRATE SCAFFOLDS - Click Chemistry in Glycoscience: New Developments and Strategies - page 119

RO

RO

O

O O

OBn OR

RO

RO

O

OR O

O RO

O

RO OR

O

O
RO

RO 1

OR

O

RO

RO N

N

O
OR

O 5

N

HO RO

O

4

O 4

104

OR O

R = ClBn

OR

Cl O

OR

RO

OR'

O OR

NaN 3 ,DMF

OR

RO O

O

O

OR

OBn

FeCl 3 ,CH 2 Cl 2

DMF, 110°C

R =ClBn, R' = Bn R= R' = H

O

OR

O

RO

106

107

O
RO

RO

OR

O

RO

O
OR

O

RO

HO RO

O

O

4

105

ORO O

R = ClBn RO

N 3 RO

O

RO

O

OR

O

1

RO N

N

5

N

RO

4

O

OR

O

OR

O

OR

RO

OR'

O OR

OR O

RO O

O

OR

FeCl 3 ,CH 2 Cl 2

R = ClBn, R' = Bn R=R'=H

108 109

SCHEME 5.25 Preparation of triazol-linked macrocycles.

After surveying the efficiency of the reaction with a variety of Cu(I) sources
(CuSO 4 , sodium ascorbate; CuSO 4 ,Cu 0 powder; Cu(I).P(OEt) 3 ; Cu(I), additives
(DBU, tris(triazolyl)amine), and solvents (DMF/H 2 O, CH 3 CN, toluene), a conve-
niently functionalized trisaccharide ( 110 ) was treated with Cu(I) and DBU in toluene
at 50 ◦ C to give the concomitant cyclodimer 111 in 80% yield. The corresponding
cyclotrimer was obtained in 15% yield (Scheme 5.26). In an extension of their work,
the authors prepared smaller macrocycles from a mono- and disaccharide, respec-
tively, able to act as molecular pores with small cavities (Scheme 5.27) [15a].
The copper-catalyzed dimerization of simple acetylated 2-propynyl and 3-butynyl
6-azido-6- deoxy-glycosides of the gluco, galacto and manno series has been reported
[44]. It was observed that the copper-catalyzed dimerizations occurred in low to
medium yields (14-54%) and showed to be dependent on the sugar moiety, the
anomeric configuration, and the size of the formed ring (Scheme 5.28). The use of