Heteroatom Exchange
2.3
261
⊡ Scheme 70
⊡ Scheme 71
cosides result in a similar 1,2-migration of the selenium group, with simultaneous installation
of a fluoride group at C-1 [113].
In another similar reaction, activation of the phenoxythiocarbonyl ester on C-2 of the thiomannoside 158 by iodonium ions leads to the anomeric thioethyl group migration to the C-2 position, yielding the 1,2-trans-glucoside 159 ( > Scheme 71) [114].
1,2-Migration and concurrent glycosidation of phenyl 2,3-O-thionocarbonyl-1-thio-α-L-rhamnopyranosides under the action of methyl trifluoromethanesulfonate (MeOTf) also give in high
yields the 3-O-(methylthio) carbonyl-2-S-phenyl-2,6-dideoxy-β-L-glucopyranosides, which
are ready precursors to the corresponding 2-deoxy-β-glycosides [115].
In the reduction of 2-azido-3-O-benzyl-4,6-O-bezylidene-2-deoxy-1-thio-β-D-mannopyranoside 160 with propane-1,3-dithiol and NEt 3 followed by the protection of the formed amino
group, migration of the ethylthio group at C-1 and the amino group at C-2 occurs with the
retention of configuration in both positions, to give 3-O-benzyl-4,6-O-bezylidene-2-S-ethyl-2thio-β-D-mannopyranosyl-(2,2,2-trichloroethoxycarbonyl)amine 161 ( > Scheme 72) [116].
⊡ Scheme 72
4.4.2 Rearrangements
When 2-deoxy-2-iodoglycosylisocyanate 162 is exposed to ammonia, a long-distance rearrangement occurs to yield 1,2-fused aminothiazoline 163 ( > Scheme 73) [117].
2.3
261
⊡ Scheme 70
⊡ Scheme 71
cosides result in a similar 1,2-migration of the selenium group, with simultaneous installation
of a fluoride group at C-1 [113].
In another similar reaction, activation of the phenoxythiocarbonyl ester on C-2 of the thiomannoside 158 by iodonium ions leads to the anomeric thioethyl group migration to the C-2 position, yielding the 1,2-trans-glucoside 159 ( > Scheme 71) [114].
1,2-Migration and concurrent glycosidation of phenyl 2,3-O-thionocarbonyl-1-thio-α-L-rhamnopyranosides under the action of methyl trifluoromethanesulfonate (MeOTf) also give in high
yields the 3-O-(methylthio) carbonyl-2-S-phenyl-2,6-dideoxy-β-L-glucopyranosides, which
are ready precursors to the corresponding 2-deoxy-β-glycosides [115].
In the reduction of 2-azido-3-O-benzyl-4,6-O-bezylidene-2-deoxy-1-thio-β-D-mannopyranoside 160 with propane-1,3-dithiol and NEt 3 followed by the protection of the formed amino
group, migration of the ethylthio group at C-1 and the amino group at C-2 occurs with the
retention of configuration in both positions, to give 3-O-benzyl-4,6-O-bezylidene-2-S-ethyl-2thio-β-D-mannopyranosyl-(2,2,2-trichloroethoxycarbonyl)amine 161 ( > Scheme 72) [116].
⊡ Scheme 72
4.4.2 Rearrangements
When 2-deoxy-2-iodoglycosylisocyanate 162 is exposed to ammonia, a long-distance rearrangement occurs to yield 1,2-fused aminothiazoline 163 ( > Scheme 73) [117].