Towards the synthesis of chiral isochromanquinones. The use of Corey–Bakshi–Shibata reductions

Abstract

(1 R,3 R,4 S)-3,4-Dihydro-4-hydroxy-6-methoxy-1,3-dimethylisochroman-5,8-dione has been synthesized in 65% ee from (1 R,3 R,4 S)-5-benzyloxy-3,4-dihydro-4-hydroxy-6-methoxy-1,3-dimethylisochroman by catalytic hydrogenolysis followed by Fremy's salt oxidation of the derived phenol. The latter isochroman was synthesized from a mercury(II) mediated oxidative cyclization of ( R)-3-benzyloxy-4-methoxy-1-(1′-hydroxyethyl)-2-prop-1′-enylbenzene which in turn was obtained in 75% ee from the chiral reduction of 1-acetyl-3-benzyloxy-4-methoxy-2-prop-1′-enylbenzene with borane–methylsulfide complex in the presence of the Corey–Bakshi–Shibata catalyst.