Brassinolide has been synthesized from stigmasterol in an overall yield of 7%. The key step in the synthesis is aldol condensation of 2α, 3α-isopropylidenedioxy-6-oxo-23, 24-dinor-5α- cholan-22-al with 3-isopropylbut-2-enolide carried out at–78° C, which gives a product with 22R, 23R stereochemistry in high yield. Catalytic hydrogenation of this product is highly stereoselective leading to the desired 24S stereochemistry in an intermediate which is ...
![(1R,3aS,3bS,5aS,6aS,9aR,10aR,10bS,12aS)-1-((S)-1-((4R,5R)-2,2-dimethyl-5-((S)-3-methylbutan-2-yl)-1,3-dioxolan-4-yl)ethyl)-8,8,10a,12a-tetramethylhexadecahydro-5H-cyclopenta[7,8]phenanthro[2,3-d][1,3]dioxol-5-one Structure](https://image.chemsrc.com/caspic/363/111118-49-1.png)