Quinidinium bromide

Dioxo-l,3-dioxanes ring-open under basic conditions. Cleavage of the 5,5-disubstituted derivatives in the presence of quininium or quinidinium alkoxides produces chiral malonic hemi-esters (ee 30-40%) in high yield [11]. The addition of cetyltrimethylammonium bromide promotes the base-catalysed cleavage of p-keto esters to form ketones under sonication [12]. 

Since heterocycles containing a trifluoromethyl group are representatives of a major structure type in agricultural and medicinal chemistry, Shibata ct al. have developed a novel enantioselective synthesis of trifluoromethyl-substituted 2-isoxazolines 46 on the basis of a domino oxa-Michael-intramolecular hemi-aminahzation-dehydration reaction of hydroxylamine with a range of ( )-trifluoromethylated enone derivatives 47 [81]. This process, which employed N-3,5-bis(trifluoromethyl)benzyl-quinidinium bromide 48 as a chiral phase-transfer catalyst combined with CsOH as a base provided a series of trifluoromethyl-substituted 2-isoxazolines 46 in high yields and enantioselectivities of up to 94% ee (Scheme 37.8). 

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