Jr. Wolf et al., SHAPE AND STEREOSELECTIVE CYCLOPROPANATION OF ALKENES CATALYZED BY IRON PORPHYRINS, Journal of the American Chemical Society, 117(36), 1995, pp. 9194-9199
Iron porphryin complexes are active catalysts for the cyclopropanation
of alkenes by ethyl diazoacetate, Fe(TTP) (TTP = meso-tetra-p-tolylpo
rphyrin), an isolated iron(II) porphyrin complex, can be used as the c
atalyst, or the iron(III) complexes of several porphyrins can be reduc
ed in situ. The reactions produce synthetically useful excesses of the
trans cyclopropyl ester products. This stereoselectivity exhibits a m
odest solvent dependence, with donor solvents giving higher ratios of
the trans cyclopropane products, The diastereoselectivity exhibits onl
y a modest dependence on the steric bulk of the porphyrin. The reactio
ns are selective for 1-alkenes and 1,1-disubstituted alkenes, Conjugat
ed substrates and enol ethers react more rapidly than simple aliphatic
alkenes, A mechanistic model for the iron-mediated reactions is propo
sed which is consistent with the data presented herein.