π-Stacked dimers in 6-meth­oxy-3,3-dimethyl-3H-benzo[f]chromene, and centrosymmetric dimers containing C—H...π(arene) hydrogen bonds in racemic 3-bromo-2,2,6,6-tetra­methyl-3,4-dihydro-2H,6H-1,5-dioxa­triphenyl­ene

The title compounds, namely 6-meth­oxy-3,3-dimethyl-3H-benzo[f]chromene, C₁₆H₁₆O₂, (III), and racemic 3-bromo-2,2,6,6-tetra­methyl-3,4-dihydro-2H,6H-1,5-dioxatriphenyl­ene, C₂₀H₂₁BrO₂, (IV), were both synthesized in one-step regioselective Wittig reactions from substituted 1,2-naphthoquinones. The new ring in both compounds adopts a screw-boat conformation. A single π–π stacking inter­action links the mol­ecules of (III) into centrosymmetric dimeric aggregates, and a single C—H...π(arene) hydrogen bond links the mol­ecules of (IV) into centrosymmetric dimers.