Oxidation of (3,4-dihydroxyphenyl)acetonitrile gives (3-hydroxy-4-oxo-cyclohexa-2,5-dienylidene)acetonitrile via the isomeric ortho -quinone ((3,4-dioxo-cyclohexa-2,5-dienylidene)acetonitrile). This para -quinomethane product is formed as a mixture of diastereoisomers and with an initial composition of Z / E 4:1. Over 24 h this mixture equilibrates to a composition of Z / E 5:4. The para -quinomethane reacts with morpholine to give (3,4-dihydroxyphenyl)-morpholin-4-yl-acetonitrile. Similar oxidation of (3,4-dihydroxynaphthalen-1-yl)acetonitrile also gives a para -quinomethane derivative and not the 1,2-naphthoquinone as previously described. The reactivity of this para -quinomethane derivative as a 1,3-dienophile in a key step of the Gates' morphine synthesis is attributed to formation of its conjugate acid.