4-Phenyl-1,2-dihydronaphthalene epoxidation

In 1998, Page and coworkers reported a series of dihydroisoquinoline-related iminium salts which can be readily synthesized in three steps from a chiral amine (Scheme 14) [140-143], Among the catalysts tested for asymmetric epoxidation, iminium salts 74 were found to be efficient catalysts (Fig. 24, Table 7, entries 2, 4-6, 17-19). Iminium salts 74a can epoxidize 4-phenyl-1,2-dihydronaphthalene in up to 63% ee (Table 7, entry 17). 

The binaphthyl-derived iminium-ion catalysts 41a and 41b were introduced by Aggarwal et al. [48a] and Page et al. [48b], respectively (Table 10.7). The highest enantioselectivities reported to date for an iminium-based olefin epoxidation -95% ee using 1-phenyl-3,4-dihydronaphthalene as substrate - were achieved with the catalyst 41b [48b]. 

Bulman Page and coworkers have optimized conditions for the use of their 5-amino-2,2-dimethyl-4-phenyl-l,3-dioxane derived imminium salt catalyst 66, and introduced two new analogues (Figure 26) for asymmetric epoxidation. 1-Phenyl cyclohexene and 1-phenyl 3,4-dihydronaphthalene are epoxidized in up to 89% ee <2007JOC4424, 2007T5386>. 

Catalyst 33a was subsequently used to epoxidize several other olefins. Again, the reactivity of the catalyst at (5 mol%) was good, but a wide range of ees was observed (Table 5.6). l-Phenyl-3,4-dihydronaphthalene was epoxidized with high enantioselectivity (95% ee and 66% yield after 35 min). 4-Phenylstyrene oxide was produced with 29% ee, one of the highest reported ees for the epoxidation of terminal alkenes using iminium salt catalysis. 

These olefins were not as reactive towards catalyst (31) as the previously tested substrate 1-phenylcyclohexene, therefore the majority of reactions were carried out at —40 °C. Again, the dichloro methane/acetonitrile conditions produce the better results in terms of both enantiomeric excess and epoxide conversion, over the dichloromethane conditions. Triphenylethylene was extremely unreactive when compared with all the other alkenes tested (entries 3, 4, 10 and 11). The best ee obtained was for l-phenyl-3,4-dihydronaphthalene at —40 °C in dichloromethane/acetonitrile, which in 3h gave 100% conversion and 65% ee. This is even more remarkable when one considers that l-phenyl-3,4-dihydro-naphthalene also gave the poorest result in dichloromethane (7% ee). 

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%... 

Catalyst ( Bu-4.33) is effective in the epoxidation of many ds-alkenes, such as the acyclic alkenes (4.42) and also cychc alkenes, especially 2,2-dimethylchromenes such as (4.43). Enhanced enantioselectivities are often observed using Katsuki s second generation catalysts (4.34) where the phenyl substituents of the BINAP moiety undergo greater steric interactions with the alkene substrate. Dihydronaphthalene (4.44) has been epoxidised with record ees using this catalyst system. ... 

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