Transformed steroids

Ionic Liquid-Promoted Wagner–Meerwein Rearrangement of 16α,17α-Epoxyandrostanes and 16α,17α-Epoxyestranes

“…The Lewis acid-catalyzed rearrangement of similar epoxides was shown to lead to 17β-methyl-Δ 13 -18-norsteroids − ,− that were obtained as side products 3a , b and 7a , b here. As interaction of the C2 proton of the imidazolium cation of the ionic liquid and the oxygen atom of an epoxide ring was detected by NMR methods by Yang et al, the formation of products 3a , b and 7a , b may follow a similar mechanism (Scheme ) to the Lewis acid-induced rearrangement.…”

“…The same reaction took place even in the absence of nucleophilic reagent. The product was identified as a 17-methyl-18-nor-5α-androstan-16-one that is an unusual rearrangement product of 1a , as the usual acid-catalyzed reaction of similar compounds was shown to lead to 16α-hydroxy-Δ 13 -18-norsteroids. − ,− The structure of 2a was proved by various spectroscopic methods including 2D NMR techniques (see below).…”

“…However, one of the most widely studied reactions of this type is the ring opening of steroidal 16α,17α-epoxides that usually leads to 18-norsteroids with a CC double bond in ring D or C. The rearranged products are formed as a result of a Wagner–Meerwein rearrangement that involves the formation of a carbocation with a 1,2-migration of the angular C-18 methyl group to C-17. The rearrangements can be induced by either a Brønsted acid ( p -toluenesulfonic acid, HF, HClO 4 , or HCOOH) or a Lewis acid (AlCl 3 , ZnCl 2 , or BF 3 ). The use of 17β-alkyl-16α,17α-epoxides usually led to the 17α-substituted 16α-hydroxy-17β-methyl-Δ 13 -18-norsteroids.…”

Bismuth(III) triflate-catalyzed rearrangement of 16α,17α-epoxy-20-oxosteroids. Synthesis and structural elucidation of new 16α-substituted 17α-alkyl-17β-methyl-Δ13-18-norsteroids

“…The formation of these epimers has been explained by an acid-catalyzed reversealdol equilibrium involving the 16-hydroxy-20-keto function of the rearranged steroid. 25 Thus, when the rearrangement is performed with substrates where the 20-keto group is absent, in both 16a,17a-epoxy-20b-hydroxypregnane and 16a,17a-epoxycholestane derivatives, using HClO 4 /MeOH 29 and HClO 4 /aqueous acetone, 30 respectively, no isomerization at C16 occurs and the corresponding 16a-hydroxy-17b-methyl-D 13 -18-nor derivatives are obtained in good yields. More recently, during an investigation related to the synthesis of the potent anti-tumour saponin OSW-1 aglycone, several 16a,17a-epoxysteroids were treated with 70% formic acid and the Wagner-Meerwein-type rearrangement took place to afford D 13 -18-norsteroids, which, in some cases, underwent subsequent lactonization between the 17a-side chain and the 16a-formyl group.…”