Stereoselective Synthesis of 1-Fluoro-exo,exo-2,6-diaryl-3,7-dioxabicyclo[3.3.0]octanes: Synthesis of (±)-1-Fluoromembrine

Abstract

Stereoselective synthesis of 1-fluoro-exo,exo-2,6-diaryl-3,7-dioxabicyclo[3.3.0]octanes is described. The synthetic strategy involves stereoselective fluorination of 3,4-trans-4,5-cis-3-aroyl-5-arylparaconic esters using Selectfluor to afford the corresponding fluorinated paraconic esters in good yields as a single isomer, which are subjected to reduction employing LiAlH4 or DIBALH followed by furofuran formation under acidic or Lewis acid conditions to afford a series of 1-fluoro-exo,exo-furofurans in moderate yields. The synthetic protocol also provides an access to (±)-1-fluoromembrine.

Synthesis of l-Ribose from d-Ribose by a Stereoconversion through Sequential Lactonization as the Key Transformation

“…The organic layer was dried (MgSO 4 ), filtered, and the solvent was evaporated. The crude product was purified by silica gel flash column chromatography to give the product as a pale yellow oil; yield 24.4 g (90%); R f = 0.2 (hexane/EtOAc = 5:1, v/v); [α] D 25 -80.00 (c 1.00, CHCl 3 ) {Lit. 26 [α] D 20 -75.00 (c 1.00, CHCl 3 )}.…”

Asymmetric Synthesis of Trifluoromethylated ent‐Fragransin C1

“…This prompts us to develop asymmetric strategy to access trifluoromethylated 2,5‐diaryltetrahydrofurans, particularly trifluoromethylated ent ‐fragransin C 1 ( 1 ), which may be of particular importance in pharmaceutical research. It is worth to note that although stereoselective syntheses of 2,5‐diaryl‐3,4‐dimethyltetrahydrofurans were available, reports addressed toward synthesis of their enantioenriched trifluoromethylated analogues are limited …”

Chiral Ferrocenyl P,N-Ligands for Palladium-Catalyzed Asymmetric Formal [3 + 2] Cycloaddition of Propargylic Esters with β-Ketoesters: Access to Functionalized Chiral 2,3-Dihydrofurans

“…The practicality of the current methodology was demonstrated by a gram-scale synthesis, followed by the transformation of the cycloadduct 3aa into the lactone 5 (Scheme ). The initial hydrogenation of 3aa predominantly generated the cis -diastereoisomer ( S , S )- 4 on the basis of the NOE experiment without any loss in enantioselectivity.…”