Synthesis of Fulvenes Using Phase-Transfer Catalysis John W. Hill, Jeffrey A. Jenson, and Joseph G. Yaritz University of Wisconsin-River Falls, River Falls, WI 54022
We have devised a new nrocedure for svnthesizine fulvenes from indene and fluorene using phase-transfer catalysis. Comnounds svntheaized include the benzhvdwlidene derivativks of fluoiene and indene and the benzilidene derivative of fluorene. Cyclopentadiene reacts readily with aldehydes and ketones in alkaline solution; iudene reacts only under more stringent conditions; and fluorene reacts only as the Grignard, sodium, or lithium derivative (1, 2). By using solid sodium hydroxide and a phase-transfer catalyst, tetrahutylammonium hydrogen sulfate, we have made these fulvene derivatives from indene and flnorene without resorting t o Grignard or alkali metal derivatives. These aldollike condensations should make interesting synthesis experiments for sophomore or advanced organic chemistry laboratories. In a typical procedure, 0.1 mole of indene (or fluorene) is dissolved in 50 mL of xylene and the solution is poured over 0.30 mole (12.0 g) of sodium hydroxide pellets in a conical flask. Then 0.01 mole (3.39 g) of tetrabutylammonium hydrogen sulfate and 1drop of water are added. Next 0.1 mole of aldehyde or ketone (benzaldehyde or benzophenone) is added, and the mixture is stirred and heated on a magnetic stirrer. Once started, the reaction is highly exothermic, and heating is discontinued. The solution a t this stage is dark green. The reaction is allowed to continue until heat is no longer evolved. The mixture is then acidified with 6 M hydrochloric acid, and the aqueous layer is separated and discarded. The solvent is removed by evaporation under diminished pressure. The crude fulvene derivative is then recrystallized from 2-propanol or ethanol. Products were identified by melting point and by infrared and nuclear magnetic resonance spectra. Indene (11.6 g, 0.1 mole) reacts with benzophenone (18.2 g, 0.1 mole) under the above conditions to form benzhydrylidene indene (22.6 g, 80% yield, m.p. 113-114 OC, lit. m.p. 114.5 OC (3))
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Journal of Chemical Education
Fluorene (17.8 g, 9.1 mole) reacts with benzophenone (18.2 g, 0.1 mole) to form benzhydrylidene fluorene (21.0 g, 65% yield, m.p. 222-4 "C, lit. m.p. 229.5 OC (4)).
Fluorene reacts with benzaldehyde (10.6 g, 10.2 mL, 0.1 mole) to form henzylidene flnorene (21.5 g, 84.6% yield, m.p. 73-75 OC, lit. m.p. 74-76 OC (5)).
Attempts t o make benzylidene indene gave an oily mixture that could not be crystallized. Control reactions without the catalyst were much slower. With fluorene, color (due to the carbanion) did not develop and no product was ohtained. With indene, some color developed, but the reaction was slow and no product was isolated. (1) Day,J. H.Chrm. Reus. 19U.54,167. (2) Bergmann,Ernst 0. Chem.Rwa. 1968.68.41; (3) Thiele,J.: Merek, K.Annolen 1918,415,237. (4) Jennings. R.J. S.;Fowler-Williams,A. J. Appl. Chem. (London) 1953.3.426, ( 5 ) Buu-Hoi. N.P.;Saint-Ruf,G. Bull.Soc.Chim.:fi. 1967,lO. 372%41.
