Furyllithium reagents

As shown in Scheme 15, 4-substituted 4-hydroxy-2,6-dimethyl-4//-pyrans 324 and 325 were obtained by reaction of 4-pyrone 322 with BuLi320 or substituted furyllithium reagents,321 respectively. 4,4-Disubstituted 2,6-dimethyl-4//-pyrans 326 were prepared by the reaction of a threefold excess of the corresponding Grignard reagents RMgX with 4-pyrone 322.3 1,316... 

We owe to Kato and his colleagues a considerable advance in furan copper reagents. They have demonstrated the formation of the lithium di(3-furyl) cuprate species 87 which is highly reactive and possesses hard properties that suit it to reaction at hard centers, mainly carbonyl carbon.223 The reagent is easily prepared in situ from 3-furyllithium and Cu2I2. Simple copper derivatives do not react with ketones, but this cuprate reacts well and quantitatively with acid chlorides. It also reacts well with some epoxides (oxirans). Moreover, there is another form prepared in the presence of... 

Why the thienyl- and furyllithium compounds attack the iodine atom instead of the p-carbon atom of alkynyliodonium ions is not entirely clear. However, they are much harder nucleophiles than the enolate salts of /Ldicarbonyl compounds and might prefer the harder iodonium center3. The much higher basicity of the heteroaryllithium reagents might also facilitate the formation of iodate ions and the displacement of alkynyllithiums from such intermediates. 

Addition of 2-furyllithium to the reagent afforded a 2 3 anti/syn ratio on addition of various zinc halides, this very modest si facial preference was overturned, resulting in an almost exclusive re-face addition. The resulting anti-addition product was parlayed into D-ribulose in four steps (eq 3). ... 

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