1,5-Dimethyl-3-methylene-4-oxo-6-oxabicyclo(3.1.0)hexane-2-carboxylic acid methyl ester 52775-89-0 6-Oxabicyclo(3.1.0)hexane-2-carboxylic acid, 1,5-dimethyl-3-methylene-4-oxo-, methyl ester