X-Ray crystal and molecular structure of a trimeric o-quinone methide derived from 2,6-dibromomethyl-4-methylphenyl

Abstract

The crystal and molecular structure of 3′-bromomethyl-5′,8-bis(methoxymethyl)-4a′,6,7′-trimethyl-2′-oxo-1′,2′,4a′,9a′-tetrahydrospiro[chroman-2,1′-xanthene], the trimerisation product obtained from 2-bromomethyl-4-methyl-6-methylenecyclohexa-2,4-dienone, an o-quinone methide formed by elimination of hydrogen bromide from 2,6-dibromomethyl-4-methylphenol, was determined by X-ray diffraction. Crystals grown from methanol were triclinic, a= 10.761 (2), b= 12.090(l), c= 10.404(2)Å, α= 101.51 (1), β= 97.49(1), γ= 87.28(1)°, space group P. The molecular structure shows that the trimerisation takes place by a twofold Diels–Alder cycloaddition in which two molecules of the original o-quinone methide, acting as heterodienes, add to a third molecule. Of the three remaining bromomethyl groups the two which are attached to an aromatic ring are converted into methoxymethyl groups during recrystallization from methanol.