Unusual Rearrangements of cis-4,7-Disubstituted 4,7-Dihydro4,7-dihydroxy[2.2]paracyclophanes on Dehydration: Stereoselective Formation of Planar Chiral Cyclohexadienones

Under acid conditions, cis-4,7-disubstituted 4,7-dihydro-4,7-dihydroxy[2.2]paracyclophanes undergo dehydration accompanied by rearrangement, affording cyclohexadienone derivatives as major products and with polysubstituted phenols being formed as minor products. The formation of either an ortho or a para semiquinoid system, as well as the configuration of the newly formed asymmetric center, depended strictly on the nature of the substituent (alkyl, allyl, or phenyl). The structures of 3,4-dihydro-3,7-dimethyl[2.2]paracyclophane-4-one (10), 3,7-diallyl-3,4-dihydro[2.2]paracyclophane-4-one (12), and 4,7-dihydro-7,8-diphenyl[2.2]paracyclophane-4-one (22) were determined by X-ray structural analysis. [2.2]Paracyclophane-4,7-quinone (1) was obtained in optically active form. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)