A POTENTIALLY GENERAL REGIOSPECIFIC SYNTHESIS OF SUBSTITUTED QUINONES FROM DIMETHYL SQUARATE

A potentially general regiospecific synthesis of benzo- and naphthoquinones is described. This method starts with dimethyl squarate (1), which is converted to the cyclobutenone ketal 3 upon sequential treatment with an organolithium reagent and then BF3 etherate or TFAA in THF/methanol. Treatment of these with a second lithium reagent followed by hydrolysis gives the cyclobutenones 5. Addition of an alkynyl-, alkenyl- or aryllithium agent to 5 followed by hydrolysis of the ketal linkage gives the corresponding 4-alkynyl- 4-alkenyl- or 4-aryl-4-hydroxycyclobutenones 7-9, and these readily rearrange to the respective quinones or hydroquinones upon thermolysis in refluxing benzene. In a similar fashion, 15 was employed as a reagent to prepare mono- and disubstituted hydroquinones and quinones.