Ethyl bioyolo [2.2.1]-hept-5-en-2-endo-oarbogylate (1) in formio aoid smoothly reaoted with paraformaldehyde in the presenoe of sulfurio acid to give a mixture, from which three components namely 4, 6 and 6 were obtained.4 and 6 were produced from a Wagner-Meerwein type rearrangement, whereas 6 was a lactonization product.The designations of their strnatnres were deduced from spectroscopic data and chemical transformations.