Reactions of polar dienes with o-quinones

Abstract

The behaviour of various types of polar dienes towards halogenated ortho quinones has been investigated in a number of representative cases. As compared to the commonly used para analogues, o-quinones provide a wide range of products that indicate a keener response to the nature, number, and position of substituents on both reactants. 3-Halogenated-o-naphthoquinones 1 and 2 react smoothly with a representative vinologous ketene acetal 3, vinylketene acetals 4 and 5, and a monooxygenated diene 6 to provide variously substituted phenanthrenequinones 7–11. Only monooxygenated dienes on the other hand add to o-benzoquinones 14–16 and give convenient syntheses of the corresponding o-naphthoquinones 18–20. Keywords: cycloaddition, o-naphthoquinones, phenanthrenequinones, regiospecificity.

Lewis Acid Catalyzed Diels−Alder Reactions of 1,2-Naphthoquinones

“…However, one class of potential dienophiles that has so far proven to be problematic are 3,4-unsubstituted 1,2-naphthoquinones . Indeed Fieser and Seligman observed that “1,2-naphthoquinone ... gives with dienes reaction mixtures of a most unpromising nature.” The challenge lies in finding conditions that promote cycloaddition without subsequent aromatization (Scheme ) . We report here on a solution to this problem through the use of Lewis acid catalysis.…”

“…The adduct 3a was accessed for the first time (i.e. without aromatization to 4 ) in 99% yield (entry 1) . Addition of 1a to isoprene ( 2b ) also gave smooth conversion to adduct 3b (entry 2).…”