Asymmetric epoxidation of 1-phenylcyclohexene

Table 7.8 Asymmetric epoxidation of 1-phenylcyclohexene utilizing protonated ammonium salts.

TABLE 5.9 Catalytic asymmetric epoxidation of 1-Phenylcyclohexene using TPPP and catalysts (24) and (Jl)"... 

TABLE 5.12 Asymmetric epoxidation of 1-Phenylcyclohexene using various solvents"... 

Scheme 10.12 Mn(salen) grafted in the nanopores of MS via flexible propyl groups resulting higher ee values for the asymmetric epoxidation of 1-phenylcyclohexene...

In addition to the original tetraphenylborate, the corresponding tetrafluoroborate, hexafluorophosphate, perchlorate and periodate salts were prepared. All of these were tested in the asymmetric catalytic epoxidation of 1-phenylcyclohexene. A catalyst loading of 5 mol% was used in a 1 1 water/acetonitrile solvent in the presence of 2 equiv of Oxone and 4 equiv of sodium carbonate at 0 °C. The enantioselectivities obtained exhibited an interesting trend. The periodate salt gave a similar ee (35%) to that of the tetraphenylborate species (40% ee), while the fluoride-containing counterions afforded lower ees (28%). The perchlorate salt also furnished inferior enantioselectivities (20% ee). All of the salts however invariably produced the same major enantiomer of the epoxide product (R,R), and all of the reactions were complete in a similar timescale (—45 min). 

Armstrong has developed a-fluoro-W-ethoxycarbonyltropinone 54 as an asymmetric catalyst for the enantio-selective epoxidation reaction 1-phenylcyclohexene oxide is produced in 97% yield and 69% ee (Scheme 20) <1998CC621>. Analogously, the use of a-acetoxy-8-oxabicyclo[3.2.1]octan-3-one 55 results in 71% yield and 98% ee (Scheme 20) <2001TA2779>. Tropinone catalyst 54 gives only low levels of enantioselectivity in the asymmetric epoxidation of dihydronaphthalene and an enol benzoate (Scheme 20) <2002JOC8610>. 

ASYMMETRIC EPOXIDATION OF trans-p-METHYLSTYRENE AND 1-PHENYLCYCLOHEXENE USING A D-FRUCTOSE-DERIVED KETONE (R,R)-trans-P-METHYLSTYRENE OXIDE AND (R,R)-l-PHENYLCYCLOHEXENE OXIDE... 

A range of structurally different chiral primary amines was converted into the corresponding iminium tetraphenylborate salts (Fig. 5.3) and tested in the asymmetric epoxidation of a standard test substrate, 1-phenylcyclohexene, using Oxone (4 equiv) as the stoichiometric oxidant, sodium carbonate (8 equiv) as base, in acetonitrile/water (2 1) at 0 °C (Table 5.1) [19,21]. 

Axial bonding of manganese-salen complexes to polystyrene containing phen-oxide or sulfonate groups yielded catalysts for the asymmetric epoxidation of styrene and styrene derivatives with NaClO/PPNO [35]. Catalyst performances were similar to the corresponding nonsupported systems and epoxide yields reached 93% with 70% ee using 1-phenylcyclohexene as substrate. Catalyst recyclability was investigated and the catalysts could be used up to three times in the epoxidation of ot-methylstyrene. 

Between 2000 and 2005, several major reviews on asymmetric organic synthesis were published [10-14] which also covered some advances in the dynamic field of polymer-immobilized manganese-saien complexes. In 2000, immobilization of Jacobsen s epoxidation catalyst [26] on polystyrene and polymethacrylate resins was reported [27]. Catalytic performances were evaluated using 1,2-dihydronaphtha-lene, indene, l-phenyl-3,4-dihydronaphthalene and 1-phenylcyclohexene as substrates, and wx-chloroperbenzoic add (m-CPBA) and N-methylmorpholine-N-oxide (NMO) as oxidant/co-oxidant. Epoxide yields up to 61% and ee values up to 91%... 

Davis has described many examples of asymmetric epoxidation mediated by oxaziridines. The first chiral oxaziildine reported was derived from bromocamphor 17, but the observed enautioselectivities were low, the best being 40% ee for 1-phenylcyclohexene oxide (Scheme 1.21) [54]. 

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