Stereocontrol in a ytterbium triflate-catalyzed 1,3-dipolar cycloaddition reaction of carbonyl ylide with N-substituted maleimides and dimethyl fumarate

The addition of Yb(OTf)(3) (10 mol%) in a Rh2(OAc)(4)-catalyzed reaction of o-(methoxycarbonyl)-alpha -diazoacetophenone with N-methylmaleimide in CH2 Cl2 or in diethyl ether gave cycloadducts with high endo-selectivity (endo: exo = 95:5-96:4). The CuOTf (20 mol%)- or CuCl-Yb(OTf)(3) (5 mol%)-catalyze d reaction also gave 1,3-dipolar cycloadducts in an endo-selective manner ( endo:exo = 94:6). On the other hand, a reaction using only Rh-2(OAc)(4) (5 mol%) as the catalyst in benzene under reflux gave cycloadducts with exo-se lectivity (endo:exo = 11:89). The reaction of N-ethyl and N-phenylmaleimide s under the same conditions showed a similar tendency in terms of the stere oselectivity.