Table 1.

Asymmetric Synthesis of Cyclobutanones by Co(II)-Catalyzed 1,4-C–H Alkylation of α-Diazoketones^a,b,c,d

^aCarried out with 1 (0.10 mmol) and [Co(P5)] (2 mol %) in TBME (0.5 mL) at 40 °C for 12 h.

^bIsolated yield.

^cDiastereomeric ratio (dr) determined by ¹H NMR analysis: trans-enriched products after purification by silica gel column chromatography due to isomerization; value in parathesis determined from reaction mixture before purification.

^dEnantiomeric excess (ee) of trans-diastereomer determined by chiral HPLC after purification.

^eReaction performed in 1.0 mmol scale.

^fAbsolute configuration determined by X-ray crystallography.

^gRelative configuration determined by X-ray crystallography.