The first one-pot synthesis of alkoxycyclopropanes via cyclometalation of styrene with Cl n AlEt 3n and RCO 2 R 0 mediated by Cp 2 ZrCl 2 Usein M. Dzhemilev * , Leila O. Khafizova, Rinat R. Gubaidullin, Leonard M. Khalilov, Askhat G. Ibragimov Institute of Petrochemistry and Catalysis, Russian Academy of Sciences, 141 Prospekt Oktyabrya, Ufa, 450075, Russia article info Article history: Received 3 July 2009 Revised 22 September 2009 Accepted 2 October 2009 Available online 8 October 2009 Keywords: Alkoxycyclopropanes Styrene Alkyl carboxylates Zr complexes Homogeneous catalysis Alkylhaloalanes Aluminum chloride abstract The one-pot cyclopropanation of styrene using Cl n AlEt 3n (Et 2 AlCl, EtAlCl 2 , AlCl 3 ) and carboxylic esters in the presence of Cp 2 ZrCl 2 as catalyst gives rise to alkoxycyclopropanes. Ó 2009 Elsevier Ltd. All rights reserved. The work reported in this Letter is a continuation of our earlier studies on chemical transformations of organoaluminum compounds (OACs) such as aluminacyclopentanes, 1–4 aluminacyclopentenes, 5,6 aluminacyclopentadienes, 7 and aluminacyclopropanes. 8,9 In order to elaborate an efficient, catalytic, one-pot method for the synthesis of substituted cyclopropanes based on a-olefins, alkylchloroalanes, and carboxylic esters, we investigated the model reactions between styrene and Et 2 AlCl, EtAlCl 2 , or AlCl 3 in the presence of ethyl acetate mediated by metallic Mg as an acceptor of chloride ions and a catalytic amount of Cp 2 ZrCl 2 . Our idea was based on the previously obtained results on cycloalumination of aryl ethylenes using EtAlCl 2 to give aluminacy- clopropanes under the action of Ti complexes. 8 The formation of phenyltitanacyclopropane from ‘Cp 2 Ti’ and styrene was the key step in this reaction. We assumed that under the chosen conditions the coordinatively unsaturated zirconocene ‘Cp 2 Zr’ would coordi- nate the styrene molecule providing intermediate phenylzircona- cyclopropane 1, transmetalation of which in situ by the OAC or AlCl 3 would then afford aluminacyclopropane 2. Subsequent reac- tion of 2 with RCO 2 R 0 at the active Al–C bond and further hydroly- sis of the reaction mixture would yield phenylcyclopropane-type compounds such as 1-ethoxy-1-methyl-2-phenylcyclopropane 3 and 1-methyl-2-phenylcyclopropanol 4 (Scheme 1). The reaction of styrene and Et 2 AlCl (1:2 ratio) catalyzed by Cp 2 ZrCl 2 (10 mol %) in the presence of metallic Mg and ethyl acetate (THF, 8 h, 20 °C styrene/[Al]/CH 3 CO 2 Et/Mg/[Zr] = 1:2:1:1.5:0.1) was shown to afford, after hydrolysis, stereoisomeric cis/trans-1-eth- oxy-1-methyl-2-phenylcyclopropanes, cis-3a and trans-3a, in a ratio of 1:1 and 52% yield (styrene conversion was 80%) (Scheme 2). 10 The 1 H and 13 C NMR spectra of the mixture of cis-3a and trans- 3a showed signals due to the ethoxy and phenyl groups as well as two characteristic singlets assigned to the methyl group [d (CH 3 ), 1.16 and 1.54, d (CH 3 ), 16.13 and 21.7]. For a reliable assignment of the signals in the NMR spectra and in order to establish the structures of the stereoisomers, homonu- clear (HH COSY) and heteronuclear (HSQC and HMBC) two-dimen- sional experiments were performed. As reference signals, the observed methyl proton resonance at 1.54 ppm correlated with the signals of the quaternary C1 carbon atom (d 62.89), the methine C2 carbon atom (d 30.6), and the methylene C3 carbon atom (d 21.0) in the HMBC experiment. In contrast, the upfield methyl group (d 1.16) interacted with the relevant carbon signals at 62.4, 29.7, and 18.0 ppm, respectively. These signals correspond to the carbon atoms of the two possible stereoisomeric cis- and trans-1-ethoxy-1-methyl-2-phenylcyclopropanes. The stereo assignments of the signals in the 1 H NMR spectra of 1,1,2-trisubsti- tuted cyclopropanes, according to specific magnitudes of the vici- nal spin-spin interaction constant (SSIC) between three protons, appeared to be rather difficult because each of the isomers should display both the cis (810 Hz) and the trans (35 Hz) vicinal con- 0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2009.10.010 * Corresponding author. Tel./fax: +7 347 2842750. E-mail address: ink@anrb.ru (U.M. Dzhemilev). Tetrahedron Letters 50 (2009) 7086–7088 Contents lists available at ScienceDirect Tetrahedron Letters journal homepage: www.elsevier.com/locate/tetlet