Dirhodium(II) Tetrakis[methyl 2-oxaazetidine-4-carboxylate]:  A Chiral Dirhodium(II) Carboxamidate of Exceptional Reactivity and Selectivity

Abstract

[formula: see text] A new chiral azetidinone-carboxylate ligand for dirhodium(II) catalysis enhances reactivity toward diazo decomposition and selectivity toward cyclopropanation enabling diazomalonates, vinyldiazoacetates, and aryldiazoacetates to be effectively used with a dirhodium(II) carboxamidate catalyst.

Enantioselective β-Lactone Formation from Phenyldiazoacetates via Catalytic Intramolecular Carbon-Hydrogen Insertion

“…However, when a tertiary C-H bond is available that could result in a g-lactone product, as is the case with isobutyl phenyldiazoacetate (13), only the g-lactone product is observed (Table 4). Here use of the chiral azetidinone-ligated catalysts gave comparable% ee values for the insertion product (14) to results from Rh 2 (S-DOSP) 4 in pentane. Clearly, the presence of a tertiary C-H bond directs C-H insertion with phenyldiazoacetates to a far greater extent than that found with diazoacetates alone.…”

“…Reactions catalyzed by chiral dirhodium(II) compounds, either the Rh 2 (S-DOSP) 4 catalyst of Davies 4 or our own chiral azetidinone-ligated catalysts, 13,14 generally resulted in b-lactone product in high yield but with only modest enantioselectivities. The use of Rh 2 (S-DOSP) 4 produced product with the highest% ee value, especially when the reaction was performed in pentane.…”

High symmetry dirhodium(II) paddlewheel complexes as chiral catalysts

“…For example, the more strained acetidinones lead to elongation of the Rh -Rh bond and hence increase the reactivity of these complexes. 53 The perspective models in Figure 13 show the C 2 -symmetry and the alignment of the ligands in the α, α, β, β-arrangement.…”

Enantioselectivity for catalytic cyclopropanation with diazomalonates

“…There are few reports of successful intermolecular cyclopropanation reactions of diazomalonates that occur with enantiocontrol, 1,2 and only a limited number have documented enantioselective intramolecular cyclopropanation reactions of allyl esters of β-ketoacetates. 3,4 There are two reasons for this.…”