Synthesis of 3,4-Dihydrospiro[2H-1-Benzopyran-2,2′-bicyclo[2.2.1]heptane] Ring System

Camphene oxide reacted with dilithiated o-methoxy-phenylacetic acid to yield selectively the exo isomer of a spiro[γ-lactone-2,2′-bicyclo[2.2.1]heptane] which was stereoselectively converted into the exo-3,4-dihydrospiro[2H-1-benzopyran-2,2′-bicyclo[2.2.1]heptane].