In the 2H-chromene series, complexation of the aromatic ring with chromium
tricarbonyl, under thermal conditions, is totally regioselective even when
aromatic substituents are introduced on the pyran ring. The complexation st
abilizes the open form of these photochromic compounds and reduces the ther
mal bleaching kinetic constant. Copyright (C) 1999 John Wiley & Sons, Ltd.