| 摘要 |
This invention is directed to methods of preparing compounds of formula (I): comprising the step of reacting a compound of formula (II): with a reagent of formula POX<SUB>3 </SUB>and silica gel at a temperature greater than about 75° C., and wherein substitutions at X, PG, A, G, R<SUB>1 </SUB>and R<SUB>4 </SUB>are set forth in the specification. |
