Reaction of 3,3-bis(chloromethyl)oxetan with tris(ethoxycarbonyl)methane yields diethyl carbonate and diethyl-2-oxaspiro[3,3]heptane-6,6-dicarboxylate (II). Reduction of this diester yields the corresponding diol (III), but longer reaction time leads to cleavage of the oxetan ring. When heated, or upon attempted acid hydrolysis, this diol (III) rearranges to the 3-oxabicyclo[3,1,1]heptane derivative (VI; X = OH) and similar rearrangement occurs with acetic anhydride or thionyl chloride. Acid hydrolysis converts the diester (II) into 3,3-bis(hydroxymethy)cyclobutane-1,1-dicarboxylic acid which rapidly cyclises to its monolactone.