The title compounds are effective catalysts for intermolecular cyclopropenation reactions of l-alkynes with diazo esters and diazo amides. Diastereoselectivities achieved from the appropriate match with d- or l-menthyl diazoacetate are 77 to greater than or equal to 94% de. Enantioselectivities up to greater than or equal to 94% ee with 3-methoxy-1-propyne and 3,3-diethoxy-1 -propyne have been obtained. Variations in these values for metal carbene additions to alkynes are associated with electronic and/or steric influences from the alkyne or carbene substituents. N,N-Dimethyldiazoacetamide provides a higher level of enantiocontrol than do diazo esters. The absolute configurations of the cyclopropene products have been established; dirhodium(II) tetrakis[methyl 2-oxopyrrolidine-5(S)-carboxylate], Rh-2(5S-MEPY)(4), produces 2-substituted-2-cyclopropene-1-carboxylates having the (S)-configuration whereas use of Rh-2(5R-MEPY)(4) provides these cyclopropene products in the (R)-configuration. Diimide reduction of these cyclopropenecarboxylates produces the cis-disubstituted cyclopropane products exclusively.