Novel Preparation of 1- and 3-Substituted Bicyclo[3.2.2]nona-3,6,8-trien-2-ones from Tropones and 2,3-Bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]heptadiene by High-Pressure Cydoaddition-Thermal Cycloreversion Procedure

The Diels–Alder adduct of tropone with 2,3-bis(methoxycarbonyl)-7-oxabicyclo[2.2.1]hepta-2,5-diene formed homobarrelenone on heating at 130 °C. Similarly prepared were 1-hydroxy-, 3-methoxy-, 1-chloro-, and 3-chlorohomobarrelenones. High-pressure cycloaddition improved the yields of the Diels–Alder adducts. In reactions of 2-methoxy- and 2-chlorotropones with the 7-oxanorbornadiene derivative, the endo-isomers were predominantly produced together with the exo-isomers.