A new route to phenanthrene derivatives

Abstract

4,5-Dimethylbenzo[1,2-c:3,4-c′]difuran (7) is a highly reactive bisdiene, which undergoes Diels-Alder reactions with a wide variety of dienophiles, including dimethyl acetylenedicarboxylate and cis-1,4-dichlorobut-2-ene, to give phenanthrene derivatives, e.g. 10 and 12, respectively, following (hydrogenation and) dehydration of the bisadducts 8 and 11, respectively. 9,10-Dimethyl-1,4:5,8-diepoxy-1,4,5,8-tetrahydro-phenanthrene (5), as a result of thermal decomposition of either (i) its bisadduct 6 with tetraphenylcyclopenta-dienone or (ii) its hydrogenated derivative 14, is a very convenient precursor of 7. © 1994.