Synthesis of 8-Hydroxy- and 11-Hydroxy-7,12-dimethylbenzanthracenes. Tin(II) Chloride Mediated Reductions

Article abstract of DOI:10.1021/jo01300a007

8-Methoxybenzanthracene-7,12-dione (3) and 11-methoxybenzanthracene-7,12-dione (4) were converted in high yields to the corresponding 7,12-bis(epoxides) (14a and 14b) (not isolated because of instability) by treatment with the ylide formed from trimethylsulfonium iodide.Reduction with lithium aluminium hydride afforded 7,12-dihydro-7,12-dihydroxy-8-methoxy-7,12-dimethylbenzanthracene (5) and 7,12-dihydro-7,12-dihydroxy-11-methoxy-7,12-dimethylbenzanthracene (6), respectively, in excellent yields.Treatment of 5 and 6 with stannous chloride and hydrogen chloride (or hydrochloric acid) in ether, ethyl acetate, dioxane, and tetrahydrofuran gave over 90percent yields of 8-methoxy-7,12-dimethylbenzanthracene (1) and 11-methoxy-7,12-dimethylbenzanthracene (2), respectively.A discussion of the mechanism of these reductions focuses on the formation of an organotin intermediate and not a free carbenium ion.