Action de l'acide p-nitroperbenzoïque et de l'eau oxygénée sur un sel d'immonium hétérocyclique stéroïdique et sur l'énamine correspondante

Asymmetric Epoxidation of cis-Alkenes Mediated by Iminium Salts: Highly Enantioselective Synthesis of Levcromakalim

“…Enantioselectivity is good to excellent; catalyst loadings, however, remain high. Oxaziridinium salts generated, for example, by oxidation of iminium salts are useful electrophilic oxidants for alkene epoxidation, and the iminium salts may be used catalytically; effective catalyst loadings can be as low as 0.1 mol %. Enantiomeric excesses obtained using chiral iminium salt catalysts have, however, until recently 6 been limited to around 70% at best.…”

Recent Advances in the Catalytic Asymmetric Reactions of Oxaziridines

“…A series of nucleophiles that include sulfides [ 22 ], sulfoxides, alkenes [ 23 ], thiolates [ 24 ], phenols [ 25 , 26 ], naphthols, enolates, silyl enol ethers, selenides [ 27 ] and C-H bonds [ 28 , 29 , 30 , 31 ] could be oxidized via an asynchronous transition state in which N-O bond cleavage is faster than C-O bond cleavage ( Figure 2 ) [ 10 ]. Oxaziridinium salt 5 , first discovered by Lusinchi and co-workers in 1976 [ 32 , 33 ], was generated by the oxidation of the corresponding iminium salt with peracid or monoperoxysulfate. It exhibits a special oxidizing power derived from the strongly electrophilic oxygen atom.…”

Atropo- and Diastereoselective Construction of Tetracyclic Biphenylazepinium Salts Derived from Aminoalcohols: Use as Catalysts in Enantioselective Asymmetric Epoxidation

“…The residue was dissolved in methanol (50 mL), NaBH 3 CN (1.23 g, 19.66 mmol, 1.2 equiv.) and acetic acid (1 mL) were added, and the solution was stirred for 16 h. Saturated aqueous NH 4 Cl (20 mL) was added, and the aqueous layer washed with Et 2 O (3 x 20 mL). The combined organic layers were washed with a saturated solution of aqueous NH 4 Cl (20 mL).…”

“…The past 30 years have seen the development of many methodologies capable of efficient asymmetric epoxidation of various types of alkene . Dioxiranes and oxaziridinium salts, first reported by Lusinchi, and generated in situ from the corresponding iminium salts or amines, have proven to be two of the most effective types of organocatalyst for asymmetric oxygen transfer to weakly nucleophilic substrates such as unfunctionalized alkenes. Over the past 10 years we have developed a range of enantiopure iminium salts effective as organocatalysts for highly enantioselective asymmetric epoxidation in the presence of Oxone as a stoichiometric oxidant.…”