| 摘要 |
A process for preparing a compound of formula (I) (See Fig. I) (in which R1 represents methyl, ethyl or isopropyl group, R2 represents a hydrogen atom or a methyl or acetyl group and R3 represents a hydrogen atom, or OR2 and R3 together with the carbon atom to which they are attached represent the group >C=0) which comprises oxidising a corresponding 23.alpha.-OH compound in the presence of a phase transfer catalyst.
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