Microwave-assisted regioselective synthesis of substituted-9-bromo-9,10-dihydro-9,10-ethanoanthracenes via Diels-Alder cycloaddition

Abstract

The substituted-9-bromo-9,10-dihydro-9,10-ethanoanthracenes ortho8a-12a and meta8b-13b have been synthesized via Diels-Alder reaction under microwave conditions. The cycloadduct isomers ortho8a-11a and meta8b-11b, with priority to ortho8a-11a, were obtained from the reaction of 9-bromoanthracene 1 with acrylonitrile 2, 2-chloroacrylonitrile 3, methacryloyl chloride 4 and acrylic acid 5, while ortho12a and meta12b, with priority to meta12b, was obtained from the reaction of 9-bromoanthracene 1 with 1-cynao vinyl acetate 6. Interestingly, the only isomer meta13b was obtained from the reaction of 9-bromoanthracene 1 with phenyl vinyl sulfone 7. The results proved that the steric or/and electronic nature of the dienophile substituent is/are playing significant roles in the regioselectivity and isomers ratio.