Solvolysis of two optically-active homoallenic tosylates, leads to cyclic products (cyclopropyl ketones and methylenecyclobutanols) with inversion of configuration at the carbon bearing the leaving group, without loss of optical activity. A kinetic study has allowed a separation of the rate in kΔ and ks terms. It is found that kΔ is always greater than ks, particularly when the allene group is methyl-substituted