Spirans. Part IX. Dimers and trimers of o-quinone methides

Weak aqueous bases transform 2-chlorornethyl-4,6-dimethylphenol mainly into the well-known trimer (IV), a xanthenspirochromanone, but to a small extent into a novel type of dimer with the methylenexanthenone structure (X). When heated, this dimer dissociates into an o-quinone methide (II) which adds to cyclo-octa-1,5-diene, to give a cyclo-octa[b][1]benzopyran derivative (XI), or to the dimer, to give a new trimer (XII) isomeric with (IV).Weak aqueous bases convert 2-chloromethylphenol into a polymer (C7H6O)12. A relation between this polymer and the dimer (X) is pointed out. The trimerisation of o-quinone methides is analysed as a sequence of two steps of which the first is relatively slow.