Stereoselective synthesis of vitamin D analogues
The present invention relates to intermediates useful for the synthesis of calcipotriol or calcipotriol monohydrate, to methods of producing said intermediates, and to methods of stereoselectively reducing said intermediates.
1. A method for producing a compound of structure IIIa or IIIb,
wherein X represents either hydrogen or OR 2 ,
and wherein R 1 and R 2 may be the same or different and represent hydrogen, or a hydroxy protecting group,
by reacting a compound of structure VII or VIII,
wherein X, R 1 and R 2 are as defined above,
with sulphur dioxide.
2. A compound of structure IIIa, IIIb, IVaa, IVab, IVba, IVbb, IVb, or mixtures thereof,
wherein X represents either hydrogen or OR 2 ,
and wherein R 1 and R 2 may be the same or different and represent hydrogen, or a hydroxy protecting group.
3. A compound according to claim 2 , wherein X represents OR 2 .
4. A compound according to claim 3 , wherein R 1 and R 2 represent alkylsilyl.
5. A compound according to claim 3 , wherein R 1 and R 2 represent tert-butyldimethylsilyl.
6. A compound according to claim 3 , wherein R 1 and R 2 represent hydrogen.