The Complete Characterization of a Rhodium Lewis Acid−Dipolarophile Complex as an Intermediate for the Enantioselective Catalytic 1,3-Dipolar Cycloaddition of <i>C</i>,<i>N</i>-Diphenylnitrone to Methacrolein

Abstract

The 1,3-dipolar cycloaddition reaction of C,N-diphenylnitrone with methacrolein is efficiently catalyzed by the rhodium diphosphine compound (SRh,RC)-[(eta5-C5Me5)Rh(R-Prophos)(H2O)](SbF6)2 [R-Prophos = (R)-(+)-1,2-bis(diphenylphosphino)-propane, 1.SbF6]; the asymmetric catalytic process occurs with reversal of regioselectivity, perfect endo selectivity, and up to 92% ee. The complete (NMR and X-ray analysis) characterization of the involved intermediate (SRh,RC)-[(eta5-C5Me5)Rh(R-Prophos)(methacrolein)](SbF6)2 (7.SbF6) allows us to interpret the observed selectivity.