Understanding Naphthoquinones: Reactions with Alkanedithiols

Abstract

Reactions of 1,4-naphthoquinone derivatives were conducted with various alkanedithiols to understand the reaction patterns between these reagents. Previous studies found that reactions with 1,2-ethanedithiol formed a ?cyclic product,? 2,3-dihydro-1,4-dithia-9,10-anthracenedione, and two ?spiro products,? 2-1?,3?-dithiacyclopentane spiro 2?-2,3-dihydro-1,4-naphthoquinone or its 3-halogeno-derivative. Acidity of the reaction medium was also found to affect the product formation, where basic conditions favored the ?cyclic product,? while acidic conditions increased the formation of the ?spiro product.? Here, we have found that temperature also affects the product formation. Reactions of 2-chloro-1,4-naphthoquinone with 1,2-ethanedithiol in acidic conditions at approximately -4˚C favored the ?spiro products.? We have concluded that ?cyclic product? formation is thermodynamically favored, while ?spiro products? are kinetically favored. In our reactions with 1,3-propanedithiol, the extended alkane chain heavily favored the formation of ?cyclic products,? even in acidic conditions. We have also isolated four different products in reacting 2-bromo-3-methyl-1,4-naphthoquinone with 1,3-propanedithiol and triethylamine, illustrating the diversity of reactions with 1,4-naphthoquinone.