Substituent effects on rates of rhodium-catalyzed allene cyclopropanation

Rates of cyclopropanation for mono- and disubstituted allenes have been measured relative to standard substrates in reaction with aryldiazoacetate esters catalyzed by Rh2(S-DOSP)4. Phenylallene derivatives exhibited a linear correlation of rate with σ+ coefficients, indicating a resonance-based effect, though the magnitude of the effect for allenes is less than that reported for other cyclopropanations. Relative reaction rates for aliphatic allenes were found to be similar to those for aryl-substituted allenes, but silicon substitution was found to give a 5- to 14-fold rate increase. The rate enhancement effect for 1-silyl allenes can partially make up for loss of rate and regioselectivity, with 1-trimethylsilyl-1,2-butadiene exhibiting high levels of enantioselectivity and diastereoselectivity in reaction with the chiral catalyst.