Photocyclisations de cétoacétals aromatiques en vue d'une approche synthétique de la crombénine

Crombenin 1 is a spiropeltogynoid compound with a spiroacetal moiety. A similar structure was synthesized starting from an orthocarbonylphenoxyisochroman by a Norrish type II photocyclisation. With an isochroman compound, the aromatic ring induces benzyl radical formation to give chiefly a bicyclic [4.3.1] derivative. However, with the introduction of electron-withdrawing or bulky substituents at C-4′, this side reaction is limited and the spiranic product becomes preponderant. Keywords: acetals, isochroman, photocyclisation, spiroacetals.