Cinchoninium quaternary salts

Epoxidation of cycloalk-2-enones by oxygen in the presence of 9-n-hexylfluorene and a quaternary ammonium salt [17, 21, 22] has been shown to proceed via the intermediate formation of the 9-hydroperoxyfluorene [21]. The catalytic use of cinchoninium salts produces the 2(S),3(S)-oxiranes in high yields with enantiomeric excesses of up to 63% [17,21,22]. 

The reaction of carbonyl substrates with oxygen in basic media has been utilized by Shioiri and co-workers to generate optically active a-hydroxy carbonyl compounds when a quaternary ammonium salt such as /V-(4-trifluoromethylphenylmethyl)cinchoninium bromide (2) is employed as a chiral catalyst102. Enantiomeric excesses up to 74% have been realized by using this simple methodology (Table 10). 

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