Asymmetric inter- and intramolecular cyclopropanations of alkenes catalyzed by rhodium D4-porphyrin : A comparison of rhodium- and ruthenium-centred catalysts

Iodo-(5,10,15,20-tetrakis(1,2,3,4,5,6,7,8-octahydro-1,4:5,8- dimethanoanthracen-9-yl)porphyrinatorhodium(III), designated as [Rh(P*)(I)], was prepared and its catalytic activity in the asymmetric cyclopropanation of alkenes with ethyl diazoacetate (EDA) was examined. High catalyst turnovers (TON >10³) and moderate enantioselectivities (up to 68% ee) were observed. However, the obtained trans/cis ratios are low. Competition experiments revealed that electron-donating substituents on styrene accelerate the cyclopropanations. The log(k_X/k_H) versus σ⁺ plot for substituted styrenes exhibits a good linearity with a small negative ρ⁺ value (-0.14). [Rh(P*)(I)] is also active in the intramolecular cyclopropanation of allyl diazoacetates. A comparison between rhodium and ruthenium porphyrin complexes was made. © 2003 Elsevier Science Ltd. All rights reserved.