New Chiral Binaphthalene-Derived Iminium Salt Organocatalysts for Asymmetric Epoxidation of Alkenes

Abstract

A series of binaphthalene-fused azepinium salts has been generated and used as organocatalysts in the asymmetric epoxidation of unfunctionalized alkenes, giving rise to ees of up to 84%.

Calixpyrrole Derivatives: “Multi Hydrogen Bond” Catalysts for γ-Butenolide Synthesis

“…Calix[4]pyrrole ( 1 ) is the simplest member of this class of receptors. As hydrogen bond donors, calixpyrroles have a potential to behave as organocatalysts in a way similar to that reported for taddols [ 4 , 5 ], binols [ 6 , 7 , 8 , 9 ], urea and thiourea derivatives [ 10 , 11 , 12 , 13 , 14 , 15 , 16 ]. Very recently we reported the first example (and proof) of this property for the hetero-Diels-Alder reaction of Danishefsky’s diene with p -nitrobenzaldehyde organocatalysed by 10α,20β-bis(4-nitrophenyl)-calix[4]pyrrole ( 3 ) [ 17 ].…”

Novel Binaphthalene-Amine Catalysts for the Asymmetric Epoxidation of Alkenes

“…This amine catalyst, while being less reactive, is comparable in enantioselectivity to our previously reported N-isopropylsubstituted iminium salt catalyst 18 (Figure 3), which afforded up to 83% ee. 16 It is noteworthy that amine 12 induced epoxidation of 1,2-dihydronaphthalene with higher ee (47%) than all other reported binaphthalene-derived amines and iminium salts to date.…”

Green Organocatalytic Oxidative Methods using Activated Ketones

“…[32] Along the lines of oxaziridines, Bulman Page and co-workers have spent most of their research in the epoxidation of alkenes by using iminium salts such as 13 and 14 ( Figure 1). [33][34][35][36][37][38][39][40][41][42][43][44][45][46][47] More recently,i n2 013, Bulman Page managed to extend the use of catalyst 15 in heterogeneousc atalysis, while showing the first resultso fk inetic resolution in the epoxidation reaction by employing iminium salt catalysis,b yw hich enantiomeric excess values of up to 99 %f or the epoxidation of racemic cischromenes could be achieved (Scheme 11). Furthermore, a new familyo fc arbohydrate-based dihydroisoquinolinium salts 14 and 16 has been reported,a nd most recently,B ulman Page and co-workersh ave developed the first examples of the asymmetrice poxidation of dihydroquinoline substrates with iminium salt catalysts (Scheme 12).…”

“…By using catalyst 35 with as ubstrate that cannotb ea ctivated by this catalyst it has been proven that the intermediate is stabilized by additional hydrogen bonds (Figure 8). [52] Finally,i n2 013, Nair and co-workers utilized quinine (36), which activates the oxidant and the substrate via as table intermediate ( Figure 9). [84] Lattanzi andc o-workers were able to match the cinchonaa lkaloid backbonew ith thioureas 37 and Scheme19.…”