α,β-Unsaturated Carboxylic Acid Derivatives. XV. The Reaction of Ethyl 3-Nitro-2-alkenoate with Bromine Azide or Bromine, and Transformations of the Products

The reaction of ethyl (Z)-3-nitro-2-alkenoate (1) with one or two equivalents of bromine azide gave a one-to-one mixture of ethyl (E)-2-azido-3-nitro-2-alkenoate (3) and 4-ethoxycarbonyl-1,2,5-oxadiazole 2-oxide (5), or ethyl 3-bromo-2,2-diazido-3-nitroalkanoate (6), respectively, and the subsequent thermal and photochemical reactions of (E)-3 gave 2-ethoxycarbonyl-3-nitro-l-azirine, together with a small amount of 5. The addition of bromine to 1, and the subsequent elimination of hydrogen bromide from the product, gave exclusively, the (Z)-2-bromo derivative (9). The reduction of 6 and 9 with diethyl phosphonate was examined, and the reaction mechanisms were discussed.