DOES NITROARYLATION OF PHENYLACETONITRILE PROCEED AS A PHASE-TRANSFER-CATALYZED PROCESS

The phase-transfer catalyzed reaction of phenylacetonitrile with 4-chloro-3-(trifluoromethyl)nitrobenzene produces 5-chloro-7-phenyl-4-(trifluoromethyl)benzisoxazole (5) not the nitroarylation product 3a as was reported by Durantini et al. (Durantini, E. N.; Chiacchiera, S. M.; Silber, J. J. J. Org. Chem. 1993, 58, 7115). The catalytic nitroarylation does not occur because the product 3a immediately forms a lipophilic carbanion which inhibits the catalytic process. The nitroarylation occurs under ion-pair extraction conditions when a stoichiometric amount of tetrabutylammonium bromide is used, whereas 2-phenylalkanenitriles are efficiently PTC nitroarylated. 4-Chloro-3-(trifluoromethyl)- and 2-chloro-5-(trifluoromethyl)nitrobenzenes enter vicarious nucleophilic substitution reactions with carbanions of chloromethyl p-tolyl sulfone. These results and formation of 5 show that carbanions add to these nitroarenes initially in positions occupied with hydrogen.