title: Synthesis of B-ring-modified steroids through BF3-promoted rearrangement/substitution of 6β-hydroxy-5,19-cyclosteroids.
abstract: The BF3·Et2O-promoted reaction of 3β-acetoxy-5,19-cyclo-pregnan-6β-ol-20-one with different nucleophiles was investigated. B-homo steroids (3β-acetoxy-B-homo-6a-β-alkoxy-pregna-5(10)-en-20-ones) were obtained with primary and secondary alcohols, while the reaction with common carboxylic acids selectively afforded the corresponding 3β-acetoxy-6β-(acyloxymethyl)-pregna-5(10)-en-20-ones. The transformations are supposed to proceed via the rearrangement of a cyclopropyl-methyl cation (bicyclobutonium) intermediate, which is regioselectively opened in dependence on the nucleophile employed. The method represents an efficient, diversity-oriented entry to new B-ring-modified steroids, which are of potential pharmaceutical relevance.
authors: Department of Chemistry, University of Cologne , Greinstr. 4, 50939 Köln, Germany.
authors: Darius P
authors: DP
authors: Kranz
authors: Slim
authors: S
authors: Chiha
authors: Aike
authors: A
authors: Meier zu Greffen
authors: Jörg-Martin
authors: JM
authors: Neudörfl
authors: Hans-Günther
authors: HG
authors: Schmalz
mesh_terms: D001880:Boranes / Q000737:chemistry*; D002264:Carboxylic Acids / Q000737:chemistry; D003525:Cyclosteroids / Q000138:chemical synthesis* / Q000737:chemistry; D015394:Molecular Structure; D011284:Pregnenolone / Q000737:chemistry*; D013256:Steroids / Q000737:chemistry*
chemical_list: C588314:3beta-acetoxy-5,19-cyclo-pregnan-6beta-ol-20-one; C588313:6beta-hydroxy-5,19-cyclosteroid; D001880:Boranes; D002264:Carboxylic Acids; D003525:Cyclosteroids; D013256:Steroids; D011284:Pregnenolone; C021274:boron trifluoride