The synthesis of XI has as its starting material the readily available 1, 2-O-isopropylidene-~- xylofuranosea (I). This was converted to crystalline 1, 2-0-isopropylidene-5-0- methoxycarbonyl-D-xylofuranose (11) by reaction with an excess of methyl chloroformate in pyridine, a procedure that takes advantage of the large difference in rate of
![(2-methoxy-3,6-dioxabicyclo[3.1.0]hex-4-yl)methanol结构式](https://image.chemsrc.com/caspic/394/4860-82-6.png)
