( ~ ~AHEDRON LETIERS Pergamon TetrahedronLetters40 (1999) 8557-8561 Cyclopropane ring formation by an SmI2 mediated cyclisation of 8-halo-ot,13-unsaturated esters Herv6 David, Carlos Afonso, Martine Bonin, Gilles Doisneau, Made-George Guillerez and Francois Guib6 * lnstitut de Chiraie Mol~culaire d'Orsay, Laboratoire de Catalyse Mol~culaire, UPRESA-8075, B,~t. 420, Universitd Paris-Sud, 91405 Orsay, France Received26 July 1999; accepted21 September1999 Abstract 8-Iodo- and 8-bromo-ct,13-unsaturated esters with various substituents at the 13- and y-positions readily cyclise to cyclopropane compounds in the presence of samarium diiodide and a proton source. © 1999 Elsevier Science Ltd. All rights reserved. Keywords: samarium;samariumcompounds;radical reactions;cyclisations; cyclopropanes. Since the seminal report by Kagan and co-workers, ! SmI2 has found many applications in synthetic organic chemistry. In particular, SmIE-mediated sequenced radical-anionic or anionic-radical reactions are of great interest for the synthesis of various carbocyclic and heterocyclic molecules, as amply demonstrated especially by Molander and co-workers. 2 Up to now, these reactions have been essentially used for the obtention of five- or six-membered rings. For instance, Molander and Harris recently described the SmI2-induced cyclisation of ~- and q-iodo-et,13-unsaturated esters to 1-carbalkoxyalkyl- substituted cyclopentane or cyclohexane derivatives. 3 In the present communication, we report that 8- iodo- and 8-bromo-ot,[~-unsaturated esters also cyclise in the presence of SmI2, leading to cyclopropane compounds. 4 O2Bn O2Bn a:X=l 1 b:X= Br 2 3 4 c:X=H In a first experiment, we found that benzyl 5-iodopent-2-enoate la reacted with SmI2 (2.5 equiv, as a 0.1 M solution in THF) in the presence of HMPA (4 equiv.) within 5 min at room temperature to give, * Corresponding author.Tel: +33-01-69-15-52-59; fax: +33-01-69-15-46-80; e-maih fraguibe@icmo.u-psud.fr 0040-4039/99/5 - see frontmatter © 1999 Elsevier Science Ltd. All rightsreserved. PII: S0040-4039(99)01816-X