合成路线1

The reaction of vitamin D2 (I) with refluxing liquid SO2 gives a mixture of the 6(R)- and 6(S)-SO2-adducts (II), which by treatment with tert-butyl-dimethylsilyl chloride (TBDMSCI) and imidazole in DMF yields the corresponding mixture of silylated adducts (III). The reaction of the mixture (III) with NaHCO3 in ethanol affords the silylated 5(E)-vitamin D2 (IV), which by oxidation with SeO2 and N-methylmorpholine N-oxide in refluxing methanol-dichloromethane is converted into a mixture of silylated 1(S)- and 1(R)-hydroxy-5(E)-vitamin D2 (V). The silylation of (V) as before, followed by crystallization in ethyl ether-ethanol gives the 1(S)-isomer of the fully silylated compound (VI), which is treated with refluxing SO2 as before to yield the mixture of the 6(R)- and 6(S)-SO2-adducts (VII). The ozonolysis of the mixture (VII) in dichloromethane-methanol at -65 C affords the corresponding mixture of the 6(R)- and 6(S)-SO2-aldehydic adducts (VIII).