Cyclization of β-ketosulfoxide—III: Synthesis of naphthalene and phenanthrene derivatives

On heating with trichloroacetic acid or trifluoroacetic acid, 2,4-dimethoxyphenethyl methylsulfinylmethyl ketone (1) cyclized to 2,3-dimethoxy-5-methylthio-6-oxo-5, 6, 7, 8-tetrahydronaphthalene (2) through an intramolecular nucleophilic substitution of a sulfonium ion intermediate (20b), while a β -ketosulfoxide having naphthalene nucleus (3) cyclized to a tetrahydrophenanthrene 4via a Pummerer rearrangement product 23. Treatment of 1 with p-toluenesulfonic acid gave a mixture of 2,3,6-trisubstituted naphthalenes (7–10), whose composition was dependent on the reaction conditions. The aromatization proceeded via2.