Tricarbonyl[(1−4-η)-2-methoxy-5-methylenecyclohexa-1,3-diene]iron (1) undergoes
1,3-dipolar
cycloaddition reaction regio-, stereo-, and chemoselectively at its exocyclic double bond, yielding a
spiro[4.5]decane system. Reactive 1,3-dipoles with low-lying
LUMO's such as nitrile oxides, ozone, diazoacetate, and
oxoallyl cation participate well in cycloaddition to give
isoxazole, ketone, pyrazoline, and cyclopentanone adducts, respectively. The complex 1 can be viewed as
the
synthetic equivalent of synthon 2 and has been illustrated for the first time as a versatile synthetic
intermediate.