The thesis is dealing with syntheses of steroids like 25-hydroxycastasterone and other up to now unknown analogs of brassinosteroids, which is a class of phytohormones. As a starting compound the protected 22-aldehyde after side-chain degradation exhibiting the typical brassinosteroid functionalization of the A/B-ring-system was used, which is available from stigmasterol according a known procedure. After that the coupling with the side-chain synthone and the stereoselective introduction of the functional groups of the side-chain to 25-hydroxycastasterone was accomplished by different paths. Successfully was the coupling of the 22-aldehyde with the lithium salt of 3-benzyloxy-3-methylbut-1-yne and functionalization of the side chain. Likewise a second method of the direct oxyfunctionalization of castasterone with methyl(triflluormethyl)dioxirane was used. By these pathways the target compound 25-hydroxycastasterone was sythesized and completely characterized. However, after coupling of the 22-aldehyde with the synthone 3-(tetrahydropyran-2'-yloxy)-3-methylbut-1-yne and further reactions, by the alkylating epoxid opening, a new alkylating rearrangement involving the tetrahydropyranyl system was observed. This reaction resulted in a new castasterone-dioxonane-derivative with a nine-membered ring system in the side chain. Furthermore, a new strategie for the side-chain construction is described. Starting from the 22-aldehyde, a 22-hydroxy-25-tetrahydropyranyloxy-23(24)-yne was synthesized. By rearrangement of this compound and elimination of the tetrahydropyranyloxy group, a 23,24-allene was obtained. After bisepoxidation of this diene structure and hydrolysis, the 24-keto function was alkylated to a methylene group. This method gave 25-hydroxy-23-epidolichosterone as a further new brassinosteroid. Subsequent hydrogenation of this 28-methylene group resulted in a mixture of 25-hydroxy-23-epicastasterone and 25-hydroxy-23,24-diepicastasterone.