Intramolecullar alkylation of phenols. Part 4. Base-catalysed cyclisation of phenolic enones. Scope and limitations

Abstract

The phenolic enones (4), (5), (8), (9), and (13) cyclise readily under acidic conditions. However, neither these nor the thin-substituted phenols (11a), (13a), (14a), and (15a) closed under basic conditions. Involvement of unfavourable equilibria is disproved. Comparison is made with related successful cyclisations of the saturated ketone (38) and aldehyde (39). Preliminary results suggest that strict stereo-electronic requirements are necessary for enone ring closure and that these conditions are not met in base-catalysed 5-Endo- and 6-Endo-Trigonal ring closures of the phenols of general type (2; n= 0 and n= 1).