Diacetylation of benehrotrenic alkenes by acetic anhydride and weak Lewis acid (ZnCl(2), BF(3)-OEt(2)) is reported. A series of gamma-benchrotrenic pyrylium salts is obtained together with the mono and the diacetylated products. The first organometallic fused rings pyrylium sails are obtained. In connection with the electron donating effect of the Cr (CO)(3) group, the influence of rings deconjugation on NMR data is discussed. Finally the reaction of acyclic and cyclic gamma-benchrotrenic pyrylium salts with nucleophiles is described. (C) 1997 Elsevier Science S.A.