Studies on intramolecular alkylation. XIII. The synthesis of 3,4-Dihydrophenanthren-2(1H)-ones from Pummerer intermediates

Abstract

1-Methylsulfinyl-4-(naphthalen-1'-yl)butan-2-ones (12)-(15) were rearranged and cyclized to the 1-methylthio-3,4-dihydrophenanthren- 2(1H)-ones (17)-(20), respectively, by trifluoroacetic anhydride. Hydrogenolysis of (18)-(20) furnished the parent ketones (9), (25) and (26). Evidence is provided to show the involvement of an Ar₁-5 route in the formation of (18) and (19), including the formation of spiro ketone (23) from sulfoxides (14) and (16). Acid catalysed cyclization of diazoketone (5) gave either phenanthren-3-one (8) or spiro ketone (10) depending on the conditions employed.