Novel Isomerization Reaction of N,N-Dimethyl-α-(methoxycarbonyl)-4-substituted- benzylammonium N-Methylides

Fluoride ion-induced desilylation of N,N-dimethyl-N-[(trimethylsilyl)methyl]-α-(methoxycarbonyl)-4-substituted benzylammonium salts (7) gave two Stevens rearrangement products:  methyl 3-(dimethylamino)-2-(4-substituted phenyl)propionates (13) from N-methylides 8, and methyl 3-(dimethylamino)-3-(4-substituted phenyl)propionates (15) from N-benzylides 10. Additional Stevens rearrangement products, methyl 2-(dimethylamino)-3-(4-substituted phenyl)propionates (16), were competitively formed from ylides 12 when the cesium fluoride used was not predried. The mechanism of the isomerization from methylides 8, which was initially generated, to 10 and 12 is discussed.