Acid-catalyzed addition of methanol to 1 occurs by rupture of the inte
rnal carbon-carbon bond of the cyclopropane to give 2 with both retent
ion and inversion at the site of electrophilic attack (4:5, 1.3:1.0).
Nucleophilic attack occurs with inversion without relaxation of the co
rner- and edge-protonated cyclopropanes to a secondary cation.