Asymmetric Rh(II)-Catalyzed Cyclopropanation of Alkenes with Diacceptor Diazo Compounds: p-Methoxyphenyl Ketone as a General Stereoselectivity Controlling Group

Abstract

Different diacceptor diazo compounds bearing an α-PMP-ketone group were found to be effective carbene precursors for the highly stereoselective Rh(2)(S-TCPTTL)(4)-catalyzed cyclopropanation of alkenes (EWG = NO(2), CN, CO(2)Me). The resulting products were readily transformed into a variety of biologically relevant enantiopure molecules, such as cyclopropane α- and β-amino acid derivatives. Different mechanistic studies carried out led to a rationale for the high diastereo- and enantioselectivity obtained, where the PMP-ketone moiety was found to play a critical role in the stereoinduction process. Additionally, the use of catalytic amounts of achiral Lewis bases to influence the enantioinduction of the reactions developed is documented.

Rh2(S-PTTL)3TPA—a mixed-ligand dirhodium(ii) catalyst for enantioselective reactions of α-alkyl-α-diazoesters

“…1 These catalysts were pioneered by Hashimoto, 2 and in recent years have opened new modes of reactivity including highly enantioselective cyclopropanation 3 , cyclopropenation 4 , and C-H functionalization 5 of α-alkyl-α-diazoesters; cyclopropanation and C-H functionalization of α-aryl- and α-vinyl- α-diazoesters 6 ; cyclopropanation of PMP-α-diazoketones, 7 and cycloadditions of β-keto-α-diazoesters 8 .…”

Ring Opening of Donor–Acceptor Cyclopropanes with N-Nucleo­philes

“…81 A similar stereo-outcome was observed employing optically active DA cyclopropanes (S)-52а-с; stereoinformation was fully preserved in 53, while inversion of configuration occurred at the C2 stereocenter of the initial cyclopropane (Scheme 22). .…”

On the Structure of Chiral Dirhodium(II) Carboxylate Catalysts: Stereoselectivity Relevance and Insights

“…In 1993, Hashimoto, Ikegami and co-workers first reported their famous complex, Rh 2 (S-PTTL) 4 [76,77], as a catalyst that manifested (along with its variants) high enantioselectivity levels in wide range of organic transformations [2,54,[78][79][80][81][82][83][84]. For example, in enantioselective [2,3]-sigmatropic rearrangement of the cyclic propargylic oxonium ylide shown in Scheme 5a, Rh 2 (S-PTTL) 4 provided the best enantioselectivity of 79% ee of the corresponding allenic bearing benzofuran-3-one product (Scheme 5a) [85].…”