Dopamine quinone chemistry: a study of the influence of amide, amidine and guanidine substituents [-NH-CX-Y] on the mode of reaction.

The influence of N-substituents on the mode of reaction of ortho-quinones generated by oxidation of N-substituted dopamine derivatives has been studied. Ortho-quinones with amide, urea or guanidine side chains are relatively stable, with evidence of rearrangement to para-quinomethanes. The N-methylthiourea derivative rapidly cyclises giving a bicyclic product . The trichloromethylamidine derivative also rapidly cyclises but in this case gives a spirocyclic derivative . In contrast to the transient formation of spirocyclic products by other ortho-quinones derived from dopamine derivatives, e.g., , the product is stable and has been isolated and fully characterised.