A Synthesis of 1-Azaanthraquinones via Diels-Alder Reaction of 4-Hydroxy- and 4-Methoxy-2-phenylquinolinequinones with 3-Trimethylsilyloxy-1, 3-butadienes : Observation of Inverse Regioselectivity

Abstract

Diels-Alder reaction of 4-hydroxy-2-phenylquinolinequinone (10a) and 4-methoxy-2-phenylquinoline-quinone (10b) with 1-methoxy-3-trimethylsilyloxybutadiene proceeded in a highly regio- and stereoselective manner to give the [4+2] adducts (11) and (14) in good yields, respectively. The structures of the adducts and their derivatives were unambiguously determined by spectroscopic data, including high resolution heteronuclear multi bond correlation. The quinolinequinones (10a and 10b) gave inverse regioselectivity. This is related to the presence of the hydroxy group or the methoxy group at the C-4 position. These results demonstrated that Diels-Alder reaction of azadienophiles with activated dienes provides a versatile method for synthesizing 4-oxygenated 1-azaanthraquinones.