Asymmetric 1,3-dipolar cycloaddition reaction between α,β-unsaturated aldehydes and nitrones catalyzed by well-defined iridium or rhodium catalysts

Reaction of the complexes (S-M,R-C)-[(eta(5)-C5Me5)M{(R)-Prophos}(H2O)](SbF6)(2) (M=Rh, Ir) with alpha,beta-unsaturated aldehydes diastereoselectively gave complexes (S-M,R-C)-[(eta(5)-C5Me5)M{(R)-Prophos}(enal)](SbF6)(2) which have been fully characterized, including an X-ray molecular structure determination of the complex (S-Rh,R-C)- [(eta(5)-C5Me5)Rh{(R)-Prophos)(trans-2-methyl-2-pentenal)](SbF6)(2). These enal complexes efficiently catalyze the enantioselective 1,3-dipolar cycloaddition of the nitrones N-benzylideneaniline N-oxide and 3,4-dihydroisoquinoline N-oxide to the corresponding enals. Reactions occur with excellent regioselectivity, perfect endo selectivity and with enantiomeric excesses up to 94%. The absolute configuration of the adduct 5-methyl-2,3-diphenylisoxazolidine-4-carboxaldehyde was determined through its (R)-(-)-alpha-methylbenzylamine derivative.