Russian Chemical Bulletin, International Edition, Vol. 57, No. 8, pp. 1661—1664, August, 2008 1661 Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1630—1633, August, 2008. 1066-5285/08/5708-1661 © 2008 Springer Science+Business Media, Inc. Synthesis of 2-cycloalkyl-4-phenylindenes and the derived ansa-zirconocenes P. V. Ivchenko and I. E. Nifant´ev Department of Chemistry, M. V. Lomonosov Moscow State University, 1 Leninskie Gory, 119992 Moscow, Russian Federation. Fax: +7 (495) 939 4523. E-mail: inpv@org.chem.msu.ru An efficient route to 2-cycloalkyl-4-phenylindenes and the corresponding ansa-zirconocenes with the —SiMe 2 — bridge was proposed. Key words: indenes, the Friedel—Crafts reaction, the Suzuki reaction, 2-cycloalkylindenes, ansa-zirconocenes, organosilicon compounds. Zirconocenes of the general formula 1 are efficient catalysts for propene polymerization. 1 Replacement of the methyl group in position 2 (compound 2) by an iso- propyl one has been found to appreciably change the catalytic properties of the complex. 2 1—4 R ZrCl 2 5, 6 Ar R´ SiMe 2 Ar R R = R´ = Me (1), cyclo-C 5 H 9 (3), cyclo-C 4 H 7 (4); R = Me, R´ = CHMe 2 (2); R = cyclo-C 5 H 9 (5), cyclo-C 4 H 7 (6). To study the influence of the geometry of zirconocene on its catalytic properties, we found it interesting to obtain ligands whose steric properties would be inter- mediate between those in compounds 1 and 2. In this context, introduction of the cyclopentyl and especially cyclobutyl fragments appeared optimal. The cyclopropyl substituent was discarded for the low stability of the three- membered ring under polymerization conditions in the presence of polymethylaluminoxane (MAO) as an elec- trophilic cocatalyst. Results and Discussion The target products were the simplest symmetric zirconocenes 3 and 4. Their possible precursors are 2-cyclo- pentyl-7-phenylindene (5) and 2-cyclobutyl-7-phenyl- indene (6), respectively. A convenient route to 2-alkyl-4- and 2-alkyl-7-aryl- indenes starts from a sodium derivative of ethyl 2-alkyl- malonate and appropriate 2-(bromomethyl)biaryl. The Scheme 1 R COOEt COOEt Ar Br a b Br Br Ar COOH R Br COOH R Ar R O Br R O ArB(OH) 2 , Pd(0) Na i i ii ii – + Reagents and conditions: i, 1) EtOH, 2) NaOH, EtOH, ∆, 3) ∆; ii, 1) SOCl 2 , CH 2 Cl 2 , 2) AlCl 3 , CH 2 Cl 2 .