iso-Propyl phenylacetate: formation of a single enolate with tBuP4 as base

Formation of the enolate of iso-propyl phenyl acetate using phosphazene bases was studied by 1H, 13C and 31P NMR. It has been shown that: (i) while EtP2 was not strong enough, tBuP4 provided the enolate and (ii) only one isomer of the enolate was formed which was assigned the Z-configuration from the stereo-outcome of the reaction. A strong conjugation between the phenyl ring and the enol moiety was observed (with ΔG12 kcal/mol as estimated by NMR) and, in the absence of air/metals, the enol was stable until +40°C. 1H and 31P NMR studies of commercially available phosphazene bases have shown that EtP2 contained less than 5% of an undetermined P2 isomer and that tBuP4 contained up to 12% of another P4 isomer whose structure has been determined.