Two new approaches to the 25-hydroxy-vitamin D2 side chain
摘要:
Two approaches to the 25-hydroxy-vitamin D2 side chain have been developed based on the solvolysis of cyclopropylcarbinyl precursors. The first involves addition of trimethylcyclopropyllithium reagent 4 to a suitably protected C/D system 9. This reaction leads directly to cyclopropylcarbinols 10a,b which can be solvolyzed to the vitamin D2 side chain directly. The second approach uses an intermediate C/D system with a side chain allylic alcohol. Cyclopropanation of the allylic alcohol using Et2Zn/CH3CHI2 produces the same type of cyclopropylcarbinols 10a,b but in differing isomer ratios. Model studies and stereochemical differences in the two approaches are discussed.