Application of the sequence halogenation/dehydrohalogenation/isomeriza
tion to alkenes 1a-g affords allenyl allylic ethers 5a-g. Thermal isom
erizations of 5a,d,e proceed by Claisen rearrangement, while 5b,c,f,g
are transformed by alternate modes of [2 + 2]cycloaddition involving b
iradical intermediates of type 19 to polycyclic structures; the variat
ions in these thermal isomerizations are mainly a function of ring siz
e.