New acceptor-substituted allenyl halides were synthesized. The addition of hydrazoic acid (HN3) to these allenyl halides led to the formation of new 1-azido-2-haloethene derivatives. The photolysis of the latter compounds afforded the corresponding 2-halo-2H-azirines. At room temperature or below, they isomerized irreversibly by [1,2]-rearrangement of halogen to form other azirine isomers in very good yields. It is the first time that such a complete rearrangement of 2-halo-2H-azirines is observed. This synthetic strategy offers the possibility to observe both azirine isomers in their pure forms from single 1-azido-2-haloethene precursor.
allenes - azides - 2-halo-2H-azirines - addition reactions - rearrangements - photochemistry - thermolysis