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)