Phosphine-Catalyzed Intramolecular Cyclizations of α‑Nitroethyl­allenoates Forming (Z)‑Furanone Oximes

A novel and efficient phosphine-catalyzed intramolecular cyclization of α-nitroethyl­allenic esters is reported. This process appears to be practical for the stereoselective syntheses of (Z)-furan-2­(3H)-one oxime derivatives in excellent yields. Mechanistically, the reaction involves a phosphine-catalyzed Michael addition of an alkylideneazinate and rearrangement of the cyclic nitronate to the α-nitroso­dihydrofuran.