Treatment of (2,7-dibromo-9H-fluoren-9-ylidene)malononitrile (1) with excesses of substituted acetylenes RC ≡ CH [R = Ph, MeC6H4, (η5-C5H5)Fe(η5- C5 H4)] 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.
Scopus Subject Areas
- Physical and Theoretical Chemistry
- Organic Chemistry
- C-C coupling
- Density functional calculations