Asymmetric Rh(II)-catalyzed cyclopropanation of alkenes with diacceptor diazo compounds: p-methoxyphenyl ketone as a general stereoselectivity controlling group.

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.