Functionalization of 9‐(Dicyanomethylene)fluorene Derivatives with Substituted Acetylenes

Abstract

AbstractTreatment of (2,7‐dibromo‐9H‐fluoren‐9‐ylidene)malononitrile (1) with excesses of substituted acetylenes RC≡CH [R = Ph, MeC6H4, (η5‐C5H5)Fe(η5‐C5H4)] under Sonogashira coupling catalytic conditions afforded novel 9‐[cyano(ethynyl)methylene]fluorene derivatives 2−4, respectively, in moderate yields. In these reactions, facile functionalization occurs at the 9‐methylene position in the fluorene, one of the cyano groups being substituted by an acetylide moiety. In order to prepare the 2,7‐diethynyl‐substituted 9‐(dicyanomethylene)fluorene compounds 8−10, palladium‐catalyzed coupling reactions between 2,7‐dibromofluoren‐9‐one and RC≡CH in a 1:2 molar ratio first have to be carried out, initially resulting in the formation of compounds 5−7 in good yields. Upon subsequent thermal treatment of 5−7 with malononitrile in DMSO, compounds 8−10 can be isolated in high purity. All attempts to obtain 8−10 from direct coupling of 1 and RC≡CH failed. Single‐crystal X‐ray structural analyses and density functional calculations have been performed on 3, 4, 7, and 8. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)