Abstract
The Diels-Alder reactions of 3,3,5-trimethyl-4-oxo-1,5-cyclo -hexadienyl trifluoromethanesulfonate 52 with several dienophiles were performed and in most of the cases cycloaddition proceeded in highly regio- and stereoselective manner to produce a single bicyclo[2.2.2]octenone derivative in good to excellent yields. Theoretical calculations based on the frontier orbital theory suggests that the HOMO of diene and the LUMO of dienophile are involved in these reactions. We have also computed the transition-state energies of the Diels-Alder reaction by ab initio RHF/STO-3G method, which supports our experimental results. The Diels-Alder adducts obtained from the above reactions were reduced using palladium catalysis (Cacchi's conditions) to furnish the products that are identical to the adducts derived from 2,6,6-trimethyl- 2,4-cyclohexadienone (28). Thus cyclohexadienyl trifluoromethane- sulfonate 52 is a stable and non-dimerizing alternative to 2,6,6-trimethyl- 2,4-cyclohexadienone (28). Our investigations clearly showed that cyclohexa-dienone 52 is a powerful diene that react with electron-deficient dienophile to produce the corresponding Diels-Alder cycloadducts, which may have great synthetic potential.