The Synthesis of 1-Phenalenones via Ring Closure Reaction of 1-Acylacy14-methylthionaphthalenes

Abstract

The acylation of 1-methylthionaphthalene [1] J with several acid anhydrides was investigated, since the direct acylation of arenethiols proceeded to S-acylation only. The reaction of [1] with an equimolar amount of acetic anhydride cata lyzed by boron trifluoride-diethyl ether complex (BF, .0Et2) afforded 1-acetyl-4-methylthionaphthalene [2 a], while the raction with excess amount of acetic anhydride gave 2-fluoro-4-methy1-6-(4 methylthio-1-naphthyl)-1, 3, 2-dioxaborinylium fluoride [3 a].1-Acy1-4-methylthionaphtahlenes [2], obtained by the re actions of acetic and propionic anhydrides with [1], reacted with propionic and butyric anhydrides to yield 4-alky1-2fluoro-6-(4-methylthio-1-naphthyl)-1, 3, 2-dioxaborinylium fluoride [3].1-Acylacy1-4-methylthionaphthalenes [4], the hydrolysis products of [3], were treated with polyphosphoric acid to produce 3-alkyl- and 2, 3-dialky1-7-methylthio-1-phenalenones [5], respectively, through the ring closure reaction in good yields. In addition, similar acylation of 1-methoxynaphthalne[6] produced 1-acy1-4-methoxynaphthalenes[7] and 4-alkyl-6-(4-methoxy-1-naphthyl)-1, 3, 2-dioxaborinylium fluoride[8]. Fur-thermore, thehydrolysis products of [8] were treated with polyphosphoric acid to produce 3-aslky- and 2, 3-dialkyl-7-methoxy-1-phenalenones [10].