Synthesis of α-bromo substituted ethyl (10-acetoxyphenanthren-9-yl)acetate and 1-(10-acetoxyphenanthren-9-yl)propan-2-one and their transformation to o-quinone methanides

Abstract

Reaction of the spiro-dioxazole 8 with phosphorus ylides 2a–c afforded the Wittig products 9a–c in high yields. Compound 9a was thermally transformed to compound 10′. Hydrogenation of compounds 9a, 9b and 9c afforded mainly compounds 14,19a and 19b, respectively, which by acetylation and bromination with NBS gave the title compounds 17 and 22. Treatment of compounds 17 and 22 with bases gave in addition to the expected o-quinone methanides 3a and 3b the methanide 28 as well. These were trapped to give compounds 4a, 5b, 6a and 29. The one-pot preparation of compound 19a from 1 and 2b and the transformation of compounds 19a, 20 and 22 into the Pechmann Dye 32 were also studied.