REVIEW 1739 Recent Advances in Indium-Promoted Organic Reactions Indium-PromotedJacques Organic Reactions Augé,* Nadège Lubin-Germain, Jacques Uziel Département de Chimie, UMR CNRS-ESCOM-Université de Cergy-Pontoise, Neuville-sur-Oise, 95031 Cergy-Pontoise, France Fax +33(1)34257071; E-mail: [email protected] Received 28 February 2007; revised 29 March 2007 2 The Oxidation States of Indium Abstract: This review deals with organic reactions which are pro- moted by indium metal or indium salts, with a focus on recent ad- vances in stoichiometric and catalytic pathways. Applications to What makes indium metal so attractive is its low first ion- transmetalations, cross-coupling reactions and carboindation, in ization potential, along with its inertness towards water which an organoindium species may be postulated, are highlighted, and its lack of toxicity.2 Table 1 gives the ionization po- as well as the reactions in which a radical is the key intermediate. tential values of some common metals.4 It turns out that Special attention is placed on the role of indium metal as a reducer, indium has a first ionization potential almost as low as that and on the Lewis acidity of indium salts in catalytic processes. of the alkali metals, much lower than that of magnesium, 1 Introduction tin, or zinc. Moreover, the advantage of indium, compared 2 The Oxidation States of Indium to aluminium, lies in its low propensity to form oxides in 3 Barbier-Type Additions air. Indium powder, when placed in a Schlenk tube for 4 Carbonyl Alkynylation 5 Carbonyl Additions via Transmetalation half an hour under gentle stirring and vacuum, gives satis- 6 Carboindation of Alkynes factory results in terms of reactivity, so that further activa- 7 Cross-Coupling Reactions tion is often unnecessary. A new protocol that uses 8 Nucleophilic Substitutions granular indium metal as a cheaper form of indium was re- 9 Radical Reactions cently introduced, but mild warming is then required.17 10 Hydroindation 11 Reduction of Functional Groups Table 1 First Ionization Potential of Some Metals 12 Activation of Silicon by Indium(III) Salts 13 Indium(III)-Catalyzed Reactions Metal Potential (eV) 14 Conclusion Lithium 5.39 Key words: indium metal, indium salts, reduction, metalation, Lewis acid Sodium 5.12 Magnesium 7.65 1 Introduction Aluminum 5.98 Indium 5.79 Indium-mediated organometallic reactions have elicited considerable attention since the discovery of the remark- Tin 7.43 1 2 able reactivity of this metal in organic or aqueous media. Zinc 9.39 Several authors have highlighted the special interest in us- ing indium metal in aqueous media as it is not affected by water or by air.3–7 Other aspects of indium(0) or indi- Indium(I) halides are insoluble in common solvents; how- um(III) chemistry were recently reviewed.8–11 Organome- ever, they rapidly disproportionate in the presence of wa- tallic species may be postulated when either indium(0) or ter:18,19 indium(I) is inserted into a carbon–halogen bond,12 but in → 3 InX 2 In + InX3 many cases, indium(0), acting as a reducing agent, may induce a radical intermediate.13 Indium(III) in the pres- The species InX (X = Br, I) and RIn (R = alkyl), original- ence of various hydrides may give rise to a powerful re- ly formed by oxidation of indium in the presence of RX in ducing agent, thereby allowing for new reactivities.14,15 the dark, may again insert into the carbon–halogen bond of RX to give a mixture of organoindium species in which Indium(III) salts are water-tolerant additives and this 20 property has resulted in an increase in the interest of using indium is in the 3+ oxidation state: such Lewis acids in catalytic processes.16 This review fo- RX + 2 In → RIn + InX cuses on the recent advances of indium-promoted organic → RX + RIn R2InX reactions, whatever the oxidation state of indium. → RX + InX RInX2 → By summation, 3 RX + 2 In R2InX + RInX2. SYNTHESIS 2007, No. 12, pp 1739–1764xx.xx.2007 The aggregation of R2InX and RInX2 gives an indium(III) Advanced online publication: 08.06.2007 sesquihalide; such a species was postulated as the reactive DOI: 10.1055/s-2007-983703; Art ID: E17807SS © Georg Thieme Verlag Stuttgart · New York intermediate in the indium(0)-mediated allylation of car- 1740 J. Augé et al. REVIEW bonyl compounds.1 When indium(I) iodide is used as the dimethylformamide, might result from the formation of a promoter in tetrahydrofuran, allylindium(III) diiodide, mixture of allylindium(I) and allylindium(III) dibromide. arising from oxidative addition, is presumably the reactive According to this hypothesis, two successive reactions species, as evidenced by the 1H NMR signal at 2.14 might occur in N,N-dimethylformamide. The fact that ppm.21 Such an oxidative addition of an indium(I) salt in only the first reaction is observed in water is probably a tetrahydrofuran solution was evidenced by a single- consequence of the rapid disproportionation of indium(I) crystal analysis of In(C6F5)Br2·2THF obtained from bro- halide in water. 22 mopentafluorobenzene and indium(I) bromide. RX + 2 In → RIn + InX Chan and Yang have carefully investigated the reaction of RX + InX → RInX indium(0) with allyl bromide.12 The 1H NMR signal at 1.7 2 → ppm observed in water was attributed to an allylindium(I) By summation, 2 RX + 2 In RIn + RInX2 species, since the same signal was observed after trans- Substrates other than alkyl halides may insert indium(I) metalation of diallylmercury with either indium or indi- halides under non-aqueous conditions. Thus, oxidative um(I) iodide. Moreover, the authors suggested that the addition of InX may occur with disulfides or diselenides, two signals observed at 1.7 and 2.15 ppm, when they per- which produce sulfides or selenides as nucleophiles in formed the reaction of allyl bromide with indium in N,N- various reactions.23 Biographical Sketches Jacques Augé graduated from the post-doctoral work with Professor Lubineau. He was promoted to Pro- Ecole Nationale Supérieure de Chim- George Whitesides at Massachusetts fessor of Organic Chemistry in 1993 ie de Paris, and received his PhD Institute of Technology in Cam- at the Université de Cergy-Pontoise. from the Université de Paris-Sud bridge, Massachusetts, he returned His current interests focus on carbo- (Orsay) in 1978, under the supervi- back to Orsay to develop aqueous or- hydrate chemistry, reaction medium sion of Professor Serge David. After ganic chemistry with Professor André effects and indium chemistry. Nadège Lubin-Germain studied or- in aqueous media and 2-keto-3- versité de Cergy-Pontoise in 1994 ganic chemistry at the Université de deoxyoctulosonic acid (KDO) syn- and joined the group of Professor J. Paris-Sud (Orsay). In 1992, she ob- thesis. After a postdoctoral fellow- Augé. Her research interests current- tained her PhD under the supervision ship with Professor C. Wandrey and ly deal with organometallic chemis- of Professor André Lubineau where Dr. Claudine Augé at the Forschung- try applied to carbohydrates. she developed projects on chemistry zentrum, Jülich, she moved to Uni- Jacques Uziel was born in Athens, sité de Cergy-Pontoise, initially in peptide synthesis in the group of Pro- Greece, in 1964. He obtained his PhD the group of Professor Sylvain Jugé, fessor Anna Maria Papini. His cur- in organic chemistry at the Université where he worked on stereogenic rent research activity deals with C- Pierre et Marie Curie (Paris VI) un- phosphorus chemistry and function- glycoside synthesis by organometal- der the supervision of Professor Jean- alized amino acid synthesis. In 2000, lic catalysis. Pierre Genêt. Since 1992, he has been he spent a year at the University of Maître de Conférences at the Univer- Florence working on solid-phase Synthesis 2007, No. 12, 1739–1764 © Thieme Stuttgart · New York REVIEW Indium-Promoted Organic Reactions 1741 HF C 2 O Both indium(I) iodide and indium(III) iodide are commer- H cially available, though in some cases it has proven better 2 HO SiR 3 O In InO Br 2 83–97% to prepare them. To accomplish this, indium(III) iodide, + Me SiO HF C SiR HF C SiR 3 2 3 3 which is very hydroscopic, is prepared as a fine yellow 2 Brook powder, from indium and iodine in xylene at reflux. Indi- 1 HF C 2 um(I) iodide is obtained by addition of indium(III) iodide rearrangement into a suspension of indium powder in xylene; the stable Scheme 2 Indium-mediated allylation of difluoroacetyltrialkyl- complex In(InI4) thus obtained is broken up by addition of silanes diethyl ether to form a mixture of insoluble indium(I) iodide and soluble indium(III) iodide.24 dihydrofurans after their indium(III)-catalyzed hydrolysis into lactols.29 Compared to other metals, indium was par- ticularly efficient in the promotion of the allylation of 3 Barbier-Type Additions fluoral methyl hemiacetal, leading to a-trifluoromethylat- ed homoallylic alcohols in water or N,N-dimethylform- 3.1 Carbonyl Allylation amide.30 The use of indium metal as a reducing agent in Barbier- With a,b-unsaturated carbonyl compounds, the indium- type carbonyl additions was first introduced by Araki and mediated allylation generally leads to the [1,2]-addition Butsugan for the allylation of carbonyl compounds in product, but in some cases the homoallylic indium alkox- 1 N,N-dimethylformamide. Considerable progress was ide intermediates undergo deoxygenative carbon–carbon made by Li and Chan, who reported the first carbonyl al- bond formation to provide cyclopropyl or a,a-diallyl de- lylation mediated by indium in water without any addi- rivatives.31 If an external nucleophile, such as a heterocy- 2 tives or special activation.