Journal of Organometallic Chemistry 559 (1998) 1 – 10 Formation of acetylenic compounds and ring transformations of 3-alkyl-3-ferrocenylcyclopropenes in the reaction with 1,3-diphenylisobenzofuran Elena I. Klimova a,c, *, Lena Ruı ´z Ramı ´rez a , Rafael Moreno Esparza a , Tatiana Klimova Berestneva a , Marcos Martinez Garcı ´a b , Natalya N. Meleshonkova c , Andrei V. Churakov c a Uniersidad Nacional Auto ´noma de Me ´xico, Facultad de Quı ´mica, Circuito Interior, Cd. Uniersitaria, Coyoaca ´n, CP 04510, Me ´xico D.F., Mexico b Uniersidad Nacional Auto ´noma de Me ´xico, Instituto de Quı ´mica, Circuito Exterior, Cd. Uniersitaria, Coyoacan, CP 04510, Me ´xico D.F., Mexico c Moscow State Uniersity M.V. Lomonoso, Chemistry Department, Vorobjoy Gory, 119899, Moscow, Russia Received 20 June 1997 Abstract The reaction of 3-ferrocenyl-3-methylcyclopropene with 1,3-diphenylisobenzofuran leads to the formation of exo - and endo -1,4-epoxy-2-ethynyl-2-ferrocenyl-1,4-diphenyltetralines as the main products in addition to the isomeric Diels – Alder exo -adducts. At the same time, 3-tert -butyl- and 3-(1-adamantyl)-3-ferrocenylcyclopropenes form the endo - and exo -adducts of 3-alkyl-1,2-(1-propene-1,3-diyl)ferrocene. The structures of the acetylenic compounds and of the adduct containing a t Bu-sub- stituent are established by X-ray structural analysis. A possible reaction pathway via intermediate zwitter-ion is discussed. © 1998 Elsevier Science S.A. All rights reserved. Keywords: Iron; Ferrocene; Cyclopropene; Three-membered ring opening; Zwitter-ion; X-ray analysis 1. Introduction In previous papers [1,2], we reported the synthesis of 3-ferrocenyl-3-methylcyclopropene 1 and the three- membered ring opening under the action of superacids: We have also noted that all our attempts to iso- late the expected product of a regular [4 +2]-cy- cloaddition of cyclopropene 1 to 1,3- diphenylisobenzofuran 3 failed. Contrary to cy- clopropene 1, 3-ferrocenyl-3-phenylcyclopropene 4 re- acts with diphenylisobenzofuran 3 to give the expected product of stereospecific [4 +2]-cycloaddi- tion 5 together with 3-ferrocenylindene 6 as a product of an intramolecular transformation of 4 [3,4]. 3-Ferrocenylindene 6 was also obtained by pro- tonation of cyclopropene 4 with superacids, followed by treatment of the reaction mixture with N,N - dimethylaniline: * Corresponding author. Fax: +52 5 6225366; e-mail: klimova@servidor.unam.mx 0022-328X/98/$19.00 © 1998 Elsevier Science S.A. All rights reserved. PII S0022-328X(97)00670-0