Spontaneous reaction of malonyl peroxides with methanol

The spontaneous reaction of disubstituted malonyl peroxides (MPOs) with methanol affording monopermalonic acid monomethyl esters is fast (minutes) for lower homologues but is sharply decelerated (days) for the higher ones. Spirocyclopropyl-MPO is an exception in which the nucleophilic opening of the spiroactivated cyclopropane ring leads to 2,4-dimethoxy-2-carboxybutanoic acid.