Chiral Dirhodium(II) Catalysts for Selective Metal Carbene Reactions

Dirhodium(II) catalysts have proven effectiveness in controlling selectivity in metal carbene reactions of diazocarbonyl compounds. Over the years many dirhodium(II) paddlewheel derivatives with chiral ligands have been advanced, but three structural classes have emerged as being most effective for inducing high stereocontrol: chiral dirhodium carboxamidates derived from cyclic chiral carboxamides and chiral dirhodium carboxylic acids derived from sybstituted chiral prolinates or from phthalimide-protected α-amino acids. This review focuses on describing which of these classes of chiral dirhodium(II) catalysts have provided the highest levels of stereocontrol in intramolecular and intermolecular reactions of diazoacetates, diazoacetoacetates and diazomalonates, vinyl- and aryldiazoacetates, and enoldiazoacetates. Assessment is taken from published results that compare catalyst results for cyclopropanation, cyclopropenation, C-H insertion, ylide formation and reactions, as well as cycloaddition reactions, especially [3+3]- and [4+3]-cycloaddition.