Pyrimidinyl mercuric acetate

Pyranose-derived glycals are also useful as substrates in C-glycosidations with pyrimidinyl mercuric acetates. As shown in Scheme 4.1.8, Farr, eta/.,7 carried out such reactions utilizing 3-O-silyl protected glycals. Palladium acetate was used as the catalyst and no salt additives were used. Compared to the results presented in the previous four schemes, the illustrated coupling proceeded cleanly with the formation of an 84% yield of a p-C-glycoside. 

As illustrated in Schemes 4.1.4 through 4.1.9, the use of pyrimidinyl mercuric acetates have been instrumental in the development of C-nucleosides. Although the comparison in Scheme 4.1.9 illustrates the utility of aryl iodides in addition to aryl mercury compounds, the nature of the specific reagents were quite different. As shown in Scheme 4.1.11, Zhang, etal.,10 utilized pyrimidinyl iodides in the preparation of C-nucleosides from furanose glycals. As illustrated, the product mixture composition was highly susceptible to the specific reaction conditions used. Thus, of the two products shown, either is available in comparable yields. 

Transition-metal-catalysed reactions of glycals with carbon nucleophiles provide an important route to C-glycosides.24 These reactions may proceed by two different pathways depending on the oxidation state of the transition metal used and the nature of the carbon nucleophile (Scheme 3.5c). For example,25 transmetallation of Pd(OAc)2 with pyrimi-dinyl mercuric acetate results in the formation of a pyrimidinyl palladium complex, which adds to the double bond of glycal derivatives. The resulting intermediate can undergo different transformations depending on the reaction conditions. 

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