Untersuchungen an 1,4-Napthochinonen, 24. Mitt.: Zur Dehalogenierung von 2-/3-Halogen-1,4-naphthochinon-derivaten

1,4-Naphthoquinones, XXIV: On the Dehalogenation of 2-/3-Halogen-1,4-naphthoquinone Derivatives Bu₃SnH is an effective reagent for the debromination of 2-bromonaphthoquinones but elimination of chlorine with 1c , e.g., only proceeds at 30%. With Et₃SiH dechlorination does not occur at all. Instead, with the 5-acetoxy derivatives 1a/1d as starting materials the cyclic acetales 3a – c are formed as selectively protected juglone derivatives. The bromo derivative 3a is obtained only at temp. < 10° and even at room temp. Br-Elimination occurs with low yield of 3b . An especially suitable reagent for the debromination of 1a – b leading to the natural compounds plumbagin ( 2a ) and isoplumbagin ( 2b ) is zinc-silver couple but Cl-elimination again occurs in traces only.