Construction of Aryliridium−Salen Complexes: Enantio- and Cis-Selective Cyclopropanation of Conjugated and Nonconjugated Olefins

Abstract

Two stable and optically active iridium-salen complexes were synthesized by introducing a tolyl or phenyl ligand at the apical position, respectively, via the S(E)Ar mechanism, and they were found to be efficient catalysts for cis-selective asymmetric cyclopropanation. The scope of the cyclopropanation was wide, and the reactions of not only conjugated mono-, di-, and trisubstituted olefins but also nonconjugated terminal olefins proceeded with high enantio- and cis-selectivity, even in the presence of a functional group such as an ether or ester. The utility of this cyclopropanation was demonstrated by a short step synthesis of 8-[(1R,2S)-2-hexylcyclopropyl]octanoate, isolated from Escherichia coli B-ATCC 11303, using the reaction as the key step.

Cyclopropanation Reactions Mediated by Group 9 Metal Porphyrin Complexes

“…Although iridium Schiff bases have been used by Katsuki et al as catalysts in cyclopropanations of olefins by diazo compounds, [102][103][104] to the best of our knowledge the catalytic efficiency of iridium porphyrins remains almost unexplored. The lack of iridium(II) porphyrin complexes as cyclopropanation catalysts may be due to their easy transformation, by reaction with simple olefins such as ethene, into iridium(III) porphyrin anionic radical species.…”

Catalytic Enantioselective Functionalization of Unactivated Terminal Alkenes

“…56 Impressively, unactivated terminal alkenes have been found to undergo selective transition metal-catalyzed cyclopropanation with many stabilized diazo compounds. Effective catalysts have been developed that are based on Co(II), 57 Cu(I), 58 Ru(II), 59 Rh(II), 60 and Ir(III) 61 complexes (major contributions are summarized in Scheme 19). The body of work in this field is large compared to that of other asymmetric transformations of terminal alkenes, and thus only a few key examples will be discussed in detail.…”

“…In 2008, Katsuki and co-workers reported an asymmetric iridium-catalyzed cis -selective cyclopropanation of nonconjugated olefins (Scheme 20). 61 Employing 1 mol% of aryliridium-salen complex 13 in the presence of ethyl α-diazoacetate and a large excess of olefin furnished cis -disubstituted cyclopropanes in high yields and excellent enantioselectivities. Of note, subsequent manipulation of the pendant ester moiety provides a straightforward method for chain extension or functional group installation.…”

Diverse engineered heme proteins enable stereodivergent cyclopropanation of unactivated alkenes

“…Unactivated, aliphatic alkenes are attractive feedstocks for chemical synthesis, but their transformation to higher-value chiral products is challenging due to their inert nature, high degree of conformational flexibility, and limited steric and electronic bias to guide stereocontrol. 17 State-of-the art methods for unactivated alkene cyclopropanation often rely on noble metals [18][19][20] (Supplemental Table S1); no iron-based catalyst for the enantioselective intermolecular cyclopropanation of unactivated alkenes has been reported. However, directed evolution of heme proteins has previously enabled biocatalysis to access reactions performed with noble-metal catalysts, such as carbonsilicon bond formation 21 and intermolecular CH amination 22 .…”