Abstract
Described herein are three types of anionic migration of silyl and stannyl groups observed during the lithiation (hydrogen-lithium exchange) of nucleosides. In the first example of 9- [2, 3, 5-tris-O- (tert-butyldimethylsilyl) -β-D-ribofuranosyl]-6-chloropurine, the 8-trimethylsilyl or 8-tributylstannyl group introduced by lithiation underwent migration to the 2-position (migration within the base) through further lithiation of the less acidic H-2. The second example was observed by using 1- (2-deoxy-D-erythro-pent-1-enofuranosyl) uracil as a substrate, wherein the lithiationbased migration took place from the 6-position of the nucleobase to the 2'-position of the sugar (furanoid glycal). The last example came from the lithiation of the 5'-O-silylated or -stannylated anti-HIV agent d 4 T (2', 3'-didehydro-3'-deoxythymidine). As a result of highly unusual vinylic lithiation in the presence of allylic hydrogen, these 5'-O-protecting groups were transferred to the 3'-position of the unsaturated sugar (migration within the sugar). Since stannyl group can be transformed in various ways, the above three examples have opened up access to nucleoside derivatives that have been difficult to be synthesized by other methods.
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