Hochdruckversuche—VIII: Die thermische isomerisierung von 1,2-diphenyl-cyclobuten-(1)-cis-3,4-dicarbonsäure-dimethyl-ester zu 3,4-diphenylmuconsäure-estern

The ring opening reaction of dimethyl-1,2-diphenyl-cyclobutene-cis-3,4-dicarboxylate (1) into (E,Z) dimethyl-3,4-diphenylmuconate (2) is accelerated 1.4 times by a pressure of 9500 atm. In addition the (Z,Z) dimethyl-3,4-diphenyl-muconate (3), forbidden by the Woodward-Hoffmann-rules, is generated. By determination of the rate constants we could show that 3 is not formed by the ring opening of 1 but by an isomerization of 2. This reaction is accelerated 11 times by a pressure of 9500 atm.