Catalytic enantioselective tandem carbonyl ylide formation-cycloaddition of α-diazo-β-ketoesters 1 (R = alkyl, n = 1,2) using 1 mol% [Rh2(S-DOSP)4] 2 in hexane at room temperature to give the cycloadducts 3 in good yields and up to 53% ee are described.
