Exploring the Substitution Reactions of Quinones: 2-Methoxy-1,4-naphthoquinone with Amines

Abstract

Constructive in the synthesis of quinone derivatives is the fact that the photochemical and thermal reactions of 2-methoxy-1,4-naphthoquinone with amines result in substitution at two different sites. The scope and limitation of these two reactions was studied by using various primary and secondary amines. The photochemical reaction was more sensitive to the degree of substitution on the nitrogen atom than the thermal reaction. All primary amines gave 2-alkylamino-3-methoxy-1,4-naphthoquinone as the major photochemical product. Secondary amines, in general, failed to produce similar photochemical products. The thermal reaction, unlike the photochemical reaction, went smoothly with both primary and secondary amines, forming 2-alkylamino-1,4-naphthoquinone by replacing the 2-methoxy group. Interestingly, in the thermal reaction with secondary amines, further dealkylation lead to unexpected products. For example, 2-methylamino-1,4-naphthoquinone is the major product in the reaction with N-methyl-isopropylamine.