SHAPE AND STEREOSELECTIVE CYCLOPROPANATION OF ALKENES CATALYZED BY IRON PORPHYRINS

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.