Improved Synthesis of 3-Methylcholanthrene

Article abstract of DOI:10.1021/jo00330a008

An improved synthesis of 7-methylindan-4-yl 1-naphthyl ketone (3), an important precursor of 3-methylcholanthrene (1), has been developed.The key intermediates for 3, 4-cyano-7-methylindan (2a) and 4-(ethoxycarbonyl)-7-methylindan (2b), were conveniently prepared in high yields by reaction of 1-(1-pyrrolidino)cyclopentene (6) with sorbonitrile (5a) or ethyl sorbate (5b), followed by aromatization with sulfur. 1-Naphthylmagnesium bromide (4b) in the presence of cuprous iodide reacted cleanly with 4-(chloromethanoyl)-7-methylindan (12) to give 3.The Friedel-Crafts acylation of naphthalene with 12 afforded 84percent of 3 and 16percent of β isomer 13.Alternatively, 3 was prepared in 75percent yield by condensation of Grignard reagent 4b with 2a in THF.Thermal annelation of 3 afforded 1 in 41.5percent yield.