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

摘要

Different diacceptor diazo compounds bearing an a-PMP-ketone group were found to be effective carbene precursors for the highly stereoselective Rh_2(S-TCPTTL)_4-catalyzed cyclopropanation of alkenes (EWG = NO2, CN, CO_2Me). 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.