Reactions at Oxygen Atoms
2.1
141
⊡ Scheme 44
Propargyloxycarbonyl as a protective group in carbohydrates
⊡ Scheme 45
Selective deprotection of 2,2,2-trichloroethoxycarbonyl group
Trichloroethoxycarbonyl groups have been installed on primary and secondary hydroxyl
groups of carbohydrate derivatives by standard coupling with 2,2,2-trichloroethyl chloroformate. It has been shown that a Troc group in the primary position of a glycosyl donor reduces
its reactivity but enhances α-selectivity in glycosylation couplings ( > Scheme 46) [276].
⊡ Scheme 46
Example of the α-orienting effect of the 6-O-Troc group