Rhodium-Mediated Enantioselective Cyclopropanation of Allenes

Reaction of monosubstituted allenes with aryldiazoacetate esters under dirhodium tetracarboxylate catalysis led to alkylidene cyclopropane products in 80−90% ee. Monosubstituted alkyl- and arylallene substrates gave 60−75% yield under standard conditions, while yields for 1,1-disubstituted allenes were significantly lower. Cyclopropanation of 1-methyl-1-(trimethylsilyl)allene proceeded in higher yield than other 1,1-disubstituted substrates, suggesting rate enhancement mediated by a significant β-silicon effect.