Nitrile-forming eliminations from oxime ethers
Abstract
The oxime ethers (7) and (8)(R = alkyl or aryl) undergo base-catalysed elimination to benzonitriles (3) in water–dioxan (4 : 1) at 25°. The Z-isomer (8Z) reacts via hydroxide-catalysed antiperiplanar elimination 70-fold more rapidly than the corresponding E-isomer. Electronic effects on syn-elimination (from 7E) show that electronwithdrawing groups aid elimination in both Ar and in the leaving group –OR; no intramolecular assistance is observed in these substrates. These results are interpreted in terms of a central E2 elimination, with appreciable C–H and N–O– bond cleavage in the transition state.
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