The synthesis of novel p-quinone methides: O-dealkylation of 5-(p-alkyloxyaryl)-10,11-dihydrodibenzo[a,d]cyclohepten-5-ols and related compounds

Article abstract of DOI:10.1002/ejoc.200400754

The synthesis of a series of novel tricyclic p-quinone methides (p-QMs) from 5-(p-alkyloxyaryl)-10,11-dihydrodibenzo[a,d]cyclohepten-5-ol and related substrates in moderate-to-good yields is reported. The reaction is proposed to proceed under mild acidic conditions by O-dealkylation of the p-alkoxy group on the p-position of the pendant 5-aryl ring on the B-ring of the tricyclic system.The effect of different alkyl groups on the oxygen atom, as well as substituent groups on the phenyl ring flanking the O-alkyl group has also been investigated The mechanism of the reaction is discussed in terms of the relatively high intermediate cation stabilities, the possible intermediacy of a hemiketal, as well as conformational effects. Various modifications to the central seven-membered B-ring to introduce more rigidity to the tricyclic system have been made and the scope of the reaction further elaborated. Furthermore, the single crystal structure of dienone 14 has been determined and the p-quinone methide shown to be non-planar, which would account for the relative conformational rigidity of these systems and their ability to accommodate the planar cyclohexa-2,5-dienone moiety and thus explain the stability of these systems relative to their 5- and six-membered B-ring counterparts. These compounds may be useful for the synthesis of novel dyes or compounds which may exhibit photochromic and thermochromic properties. ( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).