Biomimetic Synthesis of 5,6-dihydro-glaucogenin C: Construction of the Disecopregnane Skeleton by Iron(II)-Promoted Fragmentation of an α-Alkoxy Hydroperoxide
作者:Jinghan Gui、Dahai Wang、Weisheng Tian
DOI:10.1002/anie.201101893
日期:2011.7.25
A skeleton key: A biomimeticsynthesis of the title natural product was completed in 19 steps and 6.4 % overall yield. Iron(II)‐promoted fragmentation of α‐alkoxy hydroperoxide and subsequent trapping of the resulting tertiary carbon radical by iodide enabled the highly efficient construction of the challenging 13,14:14,15‐disecopregnaneskeleton (see scheme; TBDPS=tert‐butyldiphenylsilyl).
A formal synthesis of betamethasone from 5α‐pregnane‐3β,16β,20S‐triol is described. Key transformations are a bromination‐acetylation of triol, an SN2 reaction of the resulting C16α‐bromide with dimethylcopperlithium to get the required C16β‐methyl group, and a doublehydroxylation to prepare the dihydroxyacetone sidechain.
16R-Bromopregnane-3S,20S-diol reacted with potassium t-butoxide to afford androst-16-en-3S-ol in a moderate yield via fragmentation reaction. The latter is a key intermediate for the synthesis of 5 alpha-androst-16-en-3-one, as boar sex pheromone, and other steroidal drugs. In addition, 16R,20S-epoxypregnane-3S-ol was also obtained as a major product by changing the reaction solvent. (C) 2007 Elsevier Ltd. All rights reserved.