Phosphonium supported triphenylphosphine reagent: an improved access to a-fluoro-a,b-unsaturated esters Ludivine Zoute, a Ce ´line Lacombe, a Jean-Charles Quirion, a Andre ´ B. Charette b and Philippe Jubault a, * a Laboratoire d’He ´te ´rochimie Organique associe ´ au CNRS, IRCOF, INSA et Universite ´ de Rouen, 1 rue Tesnie `re, 76821 Mont Saint-Aignan Cedex, France b De ´partement de Chimie, Universite ´ de Montre ´al, PO Box 6128, Station Downtown, Que., Canada H3C 3J7 Received 19 July 2006; revised 1 September 2006; accepted 1 September 2006 Available online 25 September 2006 Abstract—a-Fluoro-a,b-unsaturated esters 2 were efficiently synthetized via diethylzinc-promoted Wittig reaction using a phospho- nium-supported triphenylphosphine SCG–PPh 3 1, which possesses similar reactivity as its parent analog triphenylphosphine. The main advantage of this system is the use of a novel low-molecular-weight support that is soluble in solvents of medium polarities for the attachment of reagents and insoluble in solvents of low polarities. Ó 2006 Elsevier Ltd. All rights reserved. 1. Introduction Very important efforts have been devoted during the past few decades towards the development of novel sup- ports to facilitate organic synthesis. This research area includes the development of insoluble 1 or soluble poly- mers 2 as solid supports, silica-bound scavengers or reagents. 3 Other approaches such as the use of ionic liquids 4 and fluorous phases 5 have been applied with success in organic synthesis. One of us recently described the synthesis of new stable entities which are soluble in well-defined solvents but that precipitate completely with a minimum amount of an orthogonal solvent. 6 Tetraarylphosphonium salts can be used effectively as solubility control group (SCG). SCG–PPh 3 1, which has been synthesized, is totally insoluble in diethyl ether, is robust and possesses similar reactivity as its parent analog triphenylphos- phine. Another unique property of 1 is its little propen- sity to trap organic compounds upon precipitation. We also recently described an efficient synthesis of fluoroolefins via diethylzinc-promoted Wittig reaction. 7 In particular, we developed an efficient synthesis of a-fluoro acrylates from aldehydes or ketones using triphenylphosphine, ethyl dibromofluoroacetate and diethylzinc. The main drawback of such a process is the difficult separation, in some cases, of triphenylphos- phine and triphenylphosphine oxide from the expected a-fluoro acrylate. We report herein the use of SCG– PPh 3 1 for the synthesis of a-fluoro-a,b-unsaturated esters (see Scheme 1). The initial process for the synthesis of such compounds was carried out in THF but SCG–Ph 3 1 presents low solubility in such a solvent. As 1 is soluble in solvents 0040-4039/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2006.09.008 Keywords: Phosphonium-supported triphenylphosphine; Wittig reac- tion; Diethylzinc; Fluorine. * Corresponding author. Fax: +33 2 35 52 29 59; e-mail: philippe. jubault@insa-rouen.fr O R 2 R 1 PPh 3 + Br 2 FCCO 2 Et + Et 2 Zn THF R 2 R 1 CO 2 Et F Ph 3 P PPh 2 ClO 4 + Br 2 FCCO 2 Et + Et 2 Zn O R 2 R 1 CH 2 Cl 2 R 2 R 1 CO 2 Et F 1 2a-j New process Initial process 2a-j Scheme 1. Tetrahedron Letters 47 (2006) 7931–7933