Epoxides, vinyl functionalized, synthesis

Another version operating under neutral conditions (Scheme 3) uses vinyl epoxides (7) as the source of the i73-allylpalladium complex 8. Here, the alkoxide is generated by opening of the epoxide simultaneously with the formation of the cationic complex. The final compound (9) possesses an alcohol functional group. This variant is very important in the synthesis of carbanucleosides. 

The introduction of functionalized two-carbon side-chains, as found in (1) and (4) has received some attention. The usual way is by reaction of a suitable keto-derivative with a vinyl Grignard reagent, followed by functionalization of the vinyl group by way of epoxidation. In this way Fraser-Reid and Walker achieved a synthesis of pillarose (2,3,6-trideoxy-4-C-hydroxyacetyl-D- /zreo-hexose) (5) from the 4-uloside (6). As an alternative method, Brimacombe s group have published details of the use of 1-methoxyvinyl lithium, which reacts with keto-compounds to give a 1-methoxy vinyl side-chain capable of functionalization in various ways. For example, Scheme 2 shows its application to 1,2 5,6-di-0-isopropylidene-a-D-n6o-hex-3-ulose. Reaction of this reagent with methyl... 

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