Synthesis of highly functionalized 9,10-anthraquinones

The reaction of dialkyl acetylenedicarboxylates with ethyl 9,10-dihydro-2-methyl-9,10-dioxo-anthracen-1-yl-carbamoyl-formate in the presence of triphenylphosphine produces dialkyl 2,5-dihydro-1-(9,10-dihydro-2-methyl-9,10-dioxoanthracen-1-yl)-4-ethoxy-5-oxo-1H-pyrrole-2,3-dicarboxylates in fairly good yields.